Thanks, consider this case closed. I did eventually recover the version myself (no thanks for Microsoft whose two support agents were less than helpful). Went into the 365 account, found the document there, opened it in Word for the Web and there were the versions (although several were still missing, I got the one I wanted).

Lesson for me: don't use Microsoft 365 or OneDrive. I've gone back to using Dropbox during a session and backing up to external drives.