A Microsoft file hosting and synchronization service.
Previously, I reported the issue was solved on my Mac with the Big Sur update.
And truly, it was. Until one day, without rhyme or reason, it wasn't again.
But I've solved the issue.
I reset my Mac to factory conditions, took out a Dropbox subscription and migrated everything from OneDrive to Dropbox.
Mind you; this didn't go without a hitch. Initially, online files from Dropbox were also taking up hard disk space.
BUT (and this is crucial): I was able to immediately start a chat with Dropbox support, which referred me to support by e-mail, after which the issue was SOLVED in 3 e-mails over the course of 3 days.
Meanwhile, over here in Microsoft-land: this thread had been going on for one-and-a-half years (which has been IGNORED by Microsoft), I've been in multiple calls with OneDrive-support and have exhausted e-mailchains with them. Without a solution. Infuriating.
My recommendation: forget OneDrive. Go to the competition.