Using MK Toon Shaders, Outline does Not Work

[Orionhart]

Hi there. This may be a failing on my understanding of how the renderer pass works, but it seems to only work with built-in materials (urp defaults). My game requires other shaders like MK Toon for stylistic rendering, and I have been able to get per-object outlines working using Rendering Layers for objects which have not yet had their new materials applied (default shaders).

How do I get this to render outlines on objects with different materials?