If you ever sign into a Microsoft account - i.e. when setting up your PC since it's nearly mandatory - Windows turns on OneDrive automatically even if you explicitly opt out of it during the setup wizard because apparently user consent doesn't mean anything. Happened to me a couple times.

I've never had it hijack the desktop/documents/pictures folder when I've explicitly disabled it, so perhaps that's a viable workaround. Ie enable OneDrive, but have it use it's own separate folders and just ignore those.

That said, really dark pattern to enable stuff users have explicitly said no to. Microsoft really is a two-headed monster these days. Parts of Windows is really good, but then there's shit like this that just ruins it.