The exact error I get says: “The OpenXR runtime requires switching to a different GPU adapter, this requires an editor restart. Do you wish to restart now (you will be prompted to save any changes)?” The options it gives are OK and Cancel. Pressing okay restarts the editor but the warning still happens. Pressing cancel or x tries to run the level but it doesn’t work properly.
I just had the same issue and then I found this answer and realized that I closed SteamVR earlier. Starting SteamVR up again worked for me.