How to reproduce:
1. Make sure you are using multiplay displays
2. Open attached Unity project 'a10-3d'
3. Move editor to a 2nd display
4. Build and run the project
5. Change your focus to 1st display (any app should be opened, for example, Chrome)
6. Wait until the build is finished
7. Observe that it runs in a background
8. Observe that you can't move your mouse cursor

Reproduced with: 2022.1.0a10.
Didn't reproduce with: 2022.1.0a9, 2021.2.b13.

Workaround: Press the Windows key to change focus.
Note: Not sure if it's the right version where this bug regressed as the issue isn't always reproducible, but couldn't reproduce it on any other version.