Running MC28 on a new M1 Mac I considered an upgrade and had just launched MC31 for the 1st time when I was called away from the Mac.
When I got back a few minutes later MC31 was scanning my Mac importing everything it could find anywhere.
That’s a NO NO.
This is intended behavior. It happens on all versions of MC, Windows, Mac, Linux, etc. It's been the norm since somewhere around MC21 or perhaps MC22.
Several people, myself included, have given their opinions that is is a bad feature. It leads to people like you feeling like something invasive has happened. In your case, you took the somewhat drastic action of deleting everything associated with MC31. I can understand why you felt that way.
So far, the MC team thinks this feature is beneficial overall and has rejected the opinions of those that think it should be disabled.
You can, of course, press the button on the interface that stops this. If you are watching and you press the button it will not run a global "search everything" import. With every new MC version that's what I do. I then import a backup from the previous version of MC. This has worked very well for me for nearly a decade of using MC.
I can't directly answer your questions about MC31. I can say that I've been using it since it came out and it seems just as good as the other MCs I've used. I would not go back to 28 personally. 31 has enough new and better behaviors. It's an evolution of the product. I can't say if it addresses your specific concerns or not, like the "white screen" behavior you described.
Best of luck to you.
Brian.