Hi, Laura!
It sounds like you've done a lot of troubleshooting already. Here are a few things you might check:
- Compatibility: Ensure URP is fully supported with your current Unity and MRTK versions. Sometimes, newer render pipelines have quirks with specific versions.
- Graphics Settings: Verify that the URP asset is correctly assigned in the Graphics settings of your project.
- Shader Compatibility: Ensure that the shaders you're using with URP are compatible with HoloLens 2.
- Build Settings: Double-check your build settings, especially the target device settings in Unity.
- Profiler: Use the Unity Profiler to diagnose where the load time is being spent. It can help pinpoint whether there's a specific step causing the delay.
- Log Files: Check the output logs from Visual Studio for any errors or warnings that might give more insight into why it's not starting.
Switching to HDRP is usually more demanding on hardware, so starting with URP is a good call.
Hopefully, one of these tips helps! Good luck!