In general, it is preferred that Pop!_OS projects are licensed GPL-3.0-only
.
There are some exceptions to this:
MPL-2.0
may be used if it is desired to allow linkage with projects that use other licenses, but require modifications to remain open sourceMIT OR Apache-2.0
may be used if it is desired to have wide use, with potential downstream modifications, in software of any license
To summarize: Use GPL-3.0-only
for applications, MPL-2.0
for libraries with utility in the open source community, and MIT OR Apache-2.0
for foundational libraries with utility anywhere.
Please use SPDX identifiers in every source file: https://spdx.dev/ids/