There's a thread on the Dropbox forums about their struggles with the Apple change.
https://www.dropboxforum.com/t5/App...3-Monterey-support/td-p/589896/highlight/true
There are posts as recently as last week. I haven't read the whole thing, but after a 5 minute perusal I came away with the understanding that Dropbox has not finished rolling out the change to support Apple's restrictions. Also, they are having problems with the new implementation and users are complaining.
It appears I'm running the old version of the software, so I'm having no trouble. I'm not sure how that software is getting around the Apple restrictions unless the restrictions are not yet fully enforced.
At this point, I'm not prepared to consider Dropbox to be a contrasting example that proves OneDrive messed up.