What happens if you create a new empty project?
You could try 2021.3.30 which just came out.
Or an earlier patch version, maybe 20, 25.
If it’s not happening with a new project it’s got to be something in your project causing this. Usually it’s an editor script or an AlwaysExecute/ExecuteInEditMode annotated script but one out of ten times, it’s a …
(sorry for the movie reference … +100 points if you get it )
I tried to use a empty project and I had the same problem.
Luckly I accidentally moved the editor from the secondary monitor to the primary monitor and, this time, a Windows Firewall pop-up appear asking me to allow a Unity sub process to proceed.
So, basically there is some bug or my Windows problem that the pop-up sourced by an app on a secondary monitor will not show it up.
I lost two works days for this stupid problem. Very annoing