A Microsoft file hosting and synchronization service.
yes, our business went from Google Business to Microsoft 365 a couple of years ago. It's been fine (if often confusing) for that time, but this has broken our whole workflow. What amazes me is that our set-up is common for a lot of small to mid businesses -- no intranet, only MS365, all work folders on OneDrive. And they have broken that! They clearly don't see OneDrive as part of their business suite.
I'm now looking at alternatives.