MM 2019: suddenly always hanging on startup

I am running MM 2019 on Windows 10 (all updates installed) and was a happy customer so far, but since about 2 weeks I again and again have the nasty effect that MM starts up almost completely, i.e. I already see the last mindmap opened, at which point the application suddenly hangs, i.e. it gets non-responsive and the cursor remains an hourglass. I tried to leave it running suspecting that it might hang in some "phone home"-activity (like update check or such) but it doesn't seem to time out. Thus the only thing one can do is to kill it.

I moved away the files it was opening. That didn't fix the issue, so it's not something in the files that it is trying to open.

I rebooted my system several times.

I then un- and re-installed MM but even that didn't fix the issue!

What could cause this?

Where are MMs registry entries? I might try to remove these to see whether it's anything in its settings.