OK did the Clean Reinstall keeping OneDrive on C, but still rooting my User folders in it. No problems so far. I'm guessing the problem was having OneDrive rooted on E then not choosing Selective Sync soon enough after the Upgrade to 9879.

Interesting how they disabled the modern Onedrive app in this version, then installed the Desktop version which appears in Control Panel. So I have what's worked for me for several years again.