The ubiquitous stuck Bimmer door, eh.
Oh the joy of removing the interior door trim on a closed door. Third car in row with the driver's rear door stuck from not being used. A classic if you don't use it you'll lose it.
This time the handle's lever was frozen to the shaft it pivots on, the return spring wasn't strong enough for the latch to return to it's neutral position so the door wouldn't open.
Removing the handle, cleaning and lubrication is all that was needed to restore operation. Well over an hour struggling to remove the panel and figure out what stuck this time. Fortunately the interior panel survived a minor brutalization intact.
It's easy to prevent this.
Lubricate whatever you can reach and work the handles, locks and latches, all of them.
In this last case the point where things seized up is absolutely inaccessible for routine lubrication but simply operating the mechanism once in a while could have prevented it from sticking.