diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 5f21424e5..c48bb6fc9 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -1727,6 +1727,9 @@ importers:
       ember-cli-4.8:
         specifier: npm:ember-cli@~4.8.0
         version: /ember-cli@4.8.1
+      ember-cli-5.12:
+        specifier: npm:ember-cli@~5.12.0
+        version: /ember-cli@5.12.0
       ember-cli-5.4:
         specifier: npm:ember-cli@~5.4.0
         version: /ember-cli@5.4.2
@@ -1790,6 +1793,9 @@ importers:
       ember-source-4.8:
         specifier: npm:ember-source@~4.8.0
         version: /ember-source@4.8.6(@babel/core@7.26.0)
+      ember-source-5.12:
+        specifier: npm:ember-source@~5.12.0
+        version: /ember-source@5.12.0
       ember-source-5.4:
         specifier: npm:ember-source@~5.4.0
         version: /ember-source@5.4.1(@babel/core@7.26.0)
diff --git a/test-packages/sample-transforms/tests/dummy/config/environment.js b/test-packages/sample-transforms/tests/dummy/config/environment.js
index 93d69f559..ca0f32bd5 100644
--- a/test-packages/sample-transforms/tests/dummy/config/environment.js
+++ b/test-packages/sample-transforms/tests/dummy/config/environment.js
@@ -11,10 +11,7 @@ module.exports = function (environment) {
         // Here you can enable experimental features on an ember canary build
         // e.g. EMBER_NATIVE_DECORATOR_SUPPORT: true
       },
-      EXTEND_PROTOTYPES: {
-        // Prevent Ember Data from overriding Date.parse.
-        Date: false,
-      },
+      EXTEND_PROTOTYPES: false,
     },
 
     APP: {
diff --git a/tests/fixtures/fastboot-app/config/environment.js b/tests/fixtures/fastboot-app/config/environment.js
index 7599ea68c..45a681a96 100644
--- a/tests/fixtures/fastboot-app/config/environment.js
+++ b/tests/fixtures/fastboot-app/config/environment.js
@@ -11,10 +11,7 @@ module.exports = function (environment) {
         // Here you can enable experimental features on an ember canary build
         // e.g. EMBER_NATIVE_DECORATOR_SUPPORT: true
       },
-      EXTEND_PROTOTYPES: {
-        // Prevent Ember Data from overriding Date.parse.
-        Date: false,
-      },
+      EXTEND_PROTOTYPES: false,
     },
     fastboot: {
       hostWhitelist: ['localhost:4200'],
diff --git a/tests/fixtures/macro-test/config/environment.js b/tests/fixtures/macro-test/config/environment.js
index c505695c0..82d921468 100644
--- a/tests/fixtures/macro-test/config/environment.js
+++ b/tests/fixtures/macro-test/config/environment.js
@@ -11,10 +11,7 @@ module.exports = function (environment) {
         // Here you can enable experimental features on an ember canary build
         // e.g. EMBER_NATIVE_DECORATOR_SUPPORT: true
       },
-      EXTEND_PROTOTYPES: {
-        // Prevent Ember Data from overriding Date.parse.
-        Date: false,
-      },
+      EXTEND_PROTOTYPES: false,
     },
 
     APP: {
diff --git a/tests/fixtures/macro-test/tests/integration/components/macro-if-test.js b/tests/fixtures/macro-test/tests/integration/components/macro-if-test.js
index 8870cc8ce..835a7707a 100644
--- a/tests/fixtures/macro-test/tests/integration/components/macro-if-test.js
+++ b/tests/fixtures/macro-test/tests/integration/components/macro-if-test.js
@@ -88,7 +88,7 @@ module('Integration | Macro | macroCondition', function (hooks) {
       assert.ok(true, 'it ran');
     };
     await render(
-      hbs`<div data-test-target {{action this.doThing}} {{macroMaybeAttrs false data-optional data-flavor="vanilla" }} ></div>`
+      hbs`<div data-test-target {{on "click" this.doThing}} {{macroMaybeAttrs false data-optional data-flavor="vanilla" }} ></div>`
     );
     let target = this.element.querySelector('[data-test-target]');
     await click(target);
diff --git a/tests/scenarios/compat-resolver-test.ts b/tests/scenarios/compat-resolver-test.ts
index d59a67b50..281cc1a1b 100644
--- a/tests/scenarios/compat-resolver-test.ts
+++ b/tests/scenarios/compat-resolver-test.ts
@@ -69,7 +69,6 @@ Scenarios.fromProject(() => new Project())
           emberVersion = '4.6.0' //based on app-template package.json
         ) {
           let etcOptions: EtcOptions = {
-            compilerPath: require.resolve('ember-source-latest/dist/ember-template-compiler'),
             targetFormat: 'hbs',
             transforms: [
               ...(extraOpts?.astPlugins ?? []),
diff --git a/tests/scenarios/compat-route-split-test.ts b/tests/scenarios/compat-route-split-test.ts
index 2b7f30ea0..181324a86 100644
--- a/tests/scenarios/compat-route-split-test.ts
+++ b/tests/scenarios/compat-route-split-test.ts
@@ -240,9 +240,7 @@ splitScenarios
               EmberENV: {
                 FEATURES: {
                 },
-                EXTEND_PROTOTYPES: {
-                  Date: false
-                }
+                EXTEND_PROTOTYPES: false,
               },
               APP: {}
             };
@@ -412,9 +410,7 @@ splitScenarios
               EmberENV: {
                 FEATURES: {
                 },
-                EXTEND_PROTOTYPES: {
-                  Date: false
-                }
+                EXTEND_PROTOTYPES: false,
               },
               APP: {}
             };
diff --git a/tests/scenarios/compat-stage2-test.ts b/tests/scenarios/compat-stage2-test.ts
index 8928ec823..290c7a051 100644
--- a/tests/scenarios/compat-stage2-test.ts
+++ b/tests/scenarios/compat-stage2-test.ts
@@ -334,6 +334,9 @@ stage2Scenarios
   });
 
 stage2Scenarios
+  // last release that supports non-colocated templates (which is part of what
+  // this test is testing)
+  .only('lts_5_12-compat-stage2-build')
   .map('static-with-rules', app => {
     app.addDependency('some-library', '1.0.0');
     app.linkDependency('@embroider/sample-transforms', { baseDir: __dirname });
diff --git a/tests/scenarios/compat-template-colocation-test.ts b/tests/scenarios/compat-template-colocation-test.ts
index c845435b8..8b978b59b 100644
--- a/tests/scenarios/compat-template-colocation-test.ts
+++ b/tests/scenarios/compat-template-colocation-test.ts
@@ -244,9 +244,7 @@ appScenarios
             EmberENV: {
               FEATURES: {
               },
-              EXTEND_PROTOTYPES: {
-                Date: false
-              }
+              EXTEND_PROTOTYPES: false,
             },
             APP: {}
           };
diff --git a/tests/scenarios/engines-test.ts b/tests/scenarios/engines-test.ts
index 4f147254b..4e7663b31 100644
--- a/tests/scenarios/engines-test.ts
+++ b/tests/scenarios/engines-test.ts
@@ -81,9 +81,7 @@ let engineScenarios = appScenarios.map('engines', project => {
 });
 
 engineScenarios
-  .skip('lts_3_28-engines') // this skip should be removed before https://github.com/embroider-build/embroider/pull/1435 is merged
-  .skip('lts_4_4-engines') // this skip should be removed before https://github.com/embroider-build/embroider/pull/1435 is merged
-  .skip('release-engines') // this skip should be removed before https://github.com/embroider-build/embroider/pull/1435 is merged
+  .skip()
   .map('without-fastboot', () => {})
   .forEachScenario(scenario => {
     Qmodule(scenario.name, function (hooks) {
@@ -137,9 +135,7 @@ engineScenarios
   });
 
 engineScenarios
-  .skip('lts_3_28-engines') // fails due to https://github.com/emberjs/ember.js/pull/20461
-  .skip('lts_4_4-engines') // fails due to https://github.com/emberjs/ember.js/pull/20461
-  .skip('release-engines') // fails due to https://github.com/emberjs/ember.js/pull/20461
+  .skip()
   .map('with-fastboot', app => {
     app.linkDependency('ember-cli-fastboot', { baseDir: __dirname });
     app.linkDependency('fastboot', { baseDir: __dirname });
diff --git a/tests/scenarios/package.json b/tests/scenarios/package.json
index 6b60d000e..1316556fd 100644
--- a/tests/scenarios/package.json
+++ b/tests/scenarios/package.json
@@ -69,6 +69,7 @@
     "ember-cli-4.8": "npm:ember-cli@~4.8.0",
     "ember-cli-5.4": "npm:ember-cli@~5.4.0",
     "ember-cli-5.8": "npm:ember-cli@~5.8.0",
+    "ember-cli-5.12": "npm:ember-cli@~5.12.0",
     "ember-cli-babel-latest": "npm:ember-cli-babel@latest",
     "ember-cli-beta": "npm:ember-cli@beta",
     "ember-cli-fastboot": "^4.1.1",
@@ -90,6 +91,7 @@
     "ember-source-4.8": "npm:ember-source@~4.8.0",
     "ember-source-5.4": "npm:ember-source@~5.4.0",
     "ember-source-5.8": "npm:ember-source@~5.8.0",
+    "ember-source-5.12": "npm:ember-source@~5.12.0",
     "ember-source-beta": "npm:ember-source@beta",
     "ember-source-canary": "https://s3.amazonaws.com/builds.emberjs.com/canary/shas/756f0e3f98b8ca5edf443fe57318b4dac692bffa.tgz",
     "ember-source-latest": "npm:ember-source@latest",
diff --git a/tests/scenarios/scenarios.ts b/tests/scenarios/scenarios.ts
index bd13ded3e..84d3d81cd 100644
--- a/tests/scenarios/scenarios.ts
+++ b/tests/scenarios/scenarios.ts
@@ -41,6 +41,14 @@ async function lts_5_8(project: Project) {
   project.linkDevDependency('@ember/test-waiters', { baseDir: __dirname, resolveName: '@ember/test-waiters' });
 }
 
+async function lts_5_12(project: Project) {
+  project.linkDevDependency('ember-source', { baseDir: __dirname, resolveName: 'ember-source-5.12' });
+  project.linkDevDependency('ember-cli', { baseDir: __dirname, resolveName: 'ember-cli-5.12' });
+  project.linkDevDependency('ember-data', { baseDir: __dirname, resolveName: 'ember-data-5.3' });
+  project.linkDevDependency('ember-cli-babel', { baseDir: __dirname, resolveName: 'ember-cli-babel-latest' });
+  project.linkDevDependency('@ember/test-waiters', { baseDir: __dirname, resolveName: '@ember/test-waiters' });
+}
+
 async function release(project: Project) {
   project.linkDevDependency('ember-source', { baseDir: __dirname, resolveName: 'ember-source-latest' });
   project.linkDevDependency('ember-cli', { baseDir: __dirname, resolveName: 'ember-cli-latest' });
@@ -72,11 +80,17 @@ async function canary(project: Project) {
 }
 
 export function supportMatrix(scenarios: Scenarios) {
-  return scenarios.expand({
-    lts_3_28,
-    lts_4_4,
-    release,
-  });
+  return (
+    scenarios
+      .expand({
+        lts_3_28,
+        lts_4_4,
+        lts_5_12,
+        release,
+      })
+      // exceeding GitHub actions limit of 256
+      .skip('lts_4_4')
+  );
 }
 
 export function fullSupportMatrix(scenarios: Scenarios) {
@@ -87,6 +101,7 @@ export function fullSupportMatrix(scenarios: Scenarios) {
     lts_4_12,
     lts_5_4,
     lts_5_8,
+    lts_5_12,
     release,
     beta,
     canary,
diff --git a/tests/scenarios/template-tag-codemod-test.ts b/tests/scenarios/template-tag-codemod-test.ts
index 1f253d250..575a7d842 100644
--- a/tests/scenarios/template-tag-codemod-test.ts
+++ b/tests/scenarios/template-tag-codemod-test.ts
@@ -6,7 +6,7 @@ import { join } from 'path';
 const { module: Qmodule, test } = QUnit;
 
 appScenarios
-  .only('release')
+  .only('lts_5_12')
   .map('template-tag-codemod', project => {
     project.mergeFiles({
       app: {
diff --git a/tests/scenarios/v2-addon-dev-test.ts b/tests/scenarios/v2-addon-dev-test.ts
index a488869a1..b359c0adb 100644
--- a/tests/scenarios/v2-addon-dev-test.ts
+++ b/tests/scenarios/v2-addon-dev-test.ts
@@ -35,7 +35,7 @@ appScenarios
             "@babel/plugin-transform-class-static-block",
             ["babel-plugin-ember-template-compilation", {
               targetFormat: 'hbs',
-              compilerPath: 'ember-source/dist/ember-template-compiler',
+              compilerPath: 'ember-source/dist/ember-template-compiler.js',
               transforms: [
                 './lib/custom-transform.js',
               ],
@@ -187,7 +187,7 @@ appScenarios
             "@babel/plugin-transform-class-static-block",
             ["babel-plugin-ember-template-compilation", {
               targetFormat: 'hbs',
-              compilerPath: 'ember-source/dist/ember-template-compiler',
+              compilerPath: 'ember-source/dist/ember-template-compiler.js',
             }],
             ["@babel/plugin-proposal-decorators", { "legacy": true }],
             [ "@babel/plugin-transform-class-properties" ]