I use three different OneDrive accounts, my personal (because I have a personal subscription to Office to allow family members also to have access to the Office applications for personal use), my work, and my university. The reason I do this is to keep the three separate, so that I'm not mixing personal with business with university, and I have three different accounts anyway, two of which are "free to me," and the other of which I'd have anyway because my family needs Office, and I can't really give them any of my work logins to use.
In any event, I had the same thing happen, and I had already updated the second of my three computers before I noticed the problem. Exactly the same thing, although I did notice that on my laptop, after I had done a lot of the things people here have described (disconnected all accounts from the computer and tried to re-add them, etc.), I could only get my personal account working again. It absolutely wouldn't let me add either of my corporate accounts, even if I disconnected all of my accounts and then tried to add one of the corporate accounts first. It would ONLY let me add back my personal account.
This is really bad for me, as I'm in the middle of a grant application that I work on sometimes while at work and sometimes while at home, using OneDrive to sync the many files that go into the application, and the deadline is Monday. It's crunch time this week. This happened at the worst possible time.
Given that it's way too cumbersome to use the web interface or copy different versions back and forth, for now I decided to move everything over to my personal OneDrive account and keep working. I have little other choice, other than to switch to a different sync client. (Believe me, I'm sorely tempted. I used to have a subscription to DropBox. Dropbox, I found, worked so much more smoothly and reliably than OneDrive, which on the Mac is buggy, frequently seems to disconnect for no apparent reason and require logging in again to one account or another to get it syncing again, etc., particularly when I'm using more than one account.)
Anyway, here's hoping Microsoft gets this fixed soon. To be honest, though, at this point, even if they fixed it today, I probably wouldn't move my files back to where they were before the update until after the grant application has been submitted next week.