Na ja, I also plan to talk to them ( Beckfish )...
I have observed something which seems to be related to the Backfish; but had so far no time to test and also not sure how I could report it.
But it seems Finder can use the directories but once in Numbers I tried to export ( to PDF ) into a directory which is Synced with O365 / OneDrive I received an error message from Numbers saying the file does not exist.
It would be just enough if Microsoft would develop something official. It is all shame a huge company can not do it.
Anyhow, explain me; keeping the O365 for Mail, for Word, and etc... why do I want to use OneDrive, instead of using iCloud Drive?
I mean for me it does not really matter if my files are stored on MS Storage, or Apple storage...