Can't open any projects in Unity 2019 - Asset Import hang

Unity's been giving us unresolvable trouble for about a year on this project, and things just hit a breaking point.
Anything requiring an asset import bricks us. I can't even get into the project. Can't switch platforms.

I'm hitting really serious unity forever-hangs/crashes with any asset import on Unity 2019.4.28f1, on even a clean install of Windows on a brand new computer after restarts and reinstalls and the whole deal. We also couldn't acquire a Unity plus license that didn't error out as "key has reached maximum number of activations, but hey, that's a separate issue.

The editor logs show zero errors or anything going wrong before hitting some random file and dying over it (usually a .wav, once a .txt file). It just goes 'not responding' and never, not after 30 minutes, nor an hour or a day progresses. Files are <40mb.

(I don't know if I can show the entire editor log because there's unannounced stuff in the filenames, but there are no errors hit anywhere, it just runs up to this and then never goes further)

If I delete the offending file, it'll just hang on the next file. There's no escaping it.
Has anyone experienced this?

And it isn't just on this project - it's on every project I have. Even ones that work fine on others' machines (all Collab)