We are sorry to say that outline shaders are not supported with URP and LWRP due to the single-pass limitation. The outline shaders draw the outline in a fist pass and the normal mesh in a second pass. This is the reason why we have not included any outline shader variants in the URP and LWRP extension packages.

Hello!
Are you going to add LWRP support for outline shader?

My posting above has become obsolete in the meantime - now both the URP and LWRP extension modules provide an outline-only shader.

Select them at your Material under the name:
Lightweight Render Pipeline/Spine/Outline/Skeleton-OutlineOnly
Universal Render Pipeline/Spine/Outline/Skeleton-OutlineOnly.

The files are located in the following subdirectory of the URP / LWRP module:
Shaders\Outline\Spine-Skeleton-OutlineOnly-LWRP.shader
Shaders\Outline\Spine-Skeleton-OutlineOnly-URP.shader

Thank you so much! It works great with RenderExistingMesh!

Thanks for getting back to us, very glad to hear it's working nicely now!