Collaboration with Sharepoint is I think the biggest issue with M365. It’s impossible to figure out where a file is stored… on your hard drive? One drive? Teams? Sharepoint?

And the biggest problem I have is managing revisions with multiple editors. If I were talking to Microsoft about strategy, this would be the thing I’d suggest. I know it’s common to use Sharepoint for collaboration, but it’s such a Frankenstein’d system that it’s going to be a problem for everyone sooner or later.