Using Unity 2019.4.16f1 on Windows 10, configured for legacy built-in XR, when I press the Play button in the editor, for some reason it opens the Windows Mixed Reality Portal and runs it in a simulator, rather than right there in the Unity IDE, but I want it to play in the IDE.
The thing is, it just randomly seemed to start doing this. I've been working for a while now with it playing in the editor, and as far as I know I didn't change any sort of configuration options. It just... always runs in the MR Portal now.
How do I configure whether it opens in the Portal vs the Unity IDE?
If you have XR enabled for a UWP app it will open either the WMR portal simulator or run on device if available.
You might have enabled 'developer mode'?
In order to disable this behavior you're going to have to disable the WMR portal simulator or disable XR support in unity. There's no other way to prevent it from opening WMR portal otherwise as far as I'm aware.