Following up with this, the issue of the error isn’t about the variant of URP not being supported. The error is happening from the warmup. It’s happening because ShaderLab has no default texture for depth texture properties, so they get assigned an rgba8 texture. The warmup function uses default values for shader properties, so the shadow texture in the shader is getting an rgba8 texture bound. Other APIs don’t care, but WebGPU is very strict. This doesn’t happen during normal renders that use the shader, just with the Warmup function. During normal renders a proper depth texture will be bound.
I will look into adding a fix that will keep the Warmup function from doing this because unneeded error messages are never good. But know that it shouldn’t be an issue with the actual use of the shader.
While we’re on the subject of ShaderVariantCollection::Warmup, it’s not the best method to do shader warmups for WebGPU (or Vulkan or DX12 for that matter). There are reasons for that, I’ll not bore you with for now. A better solution will eventually be GraphicsStateCollection, Prevent shader compilation stutters with PSO Tracing in Unity 6, but we haven’t gotten to implementing that for WebGPU yet. It’s on our near term plans.