Big Sur Bootcamp stuck partitioning
Can you give the response of the terminal command :
diskutil list

To see if there is something done by BootCamp
Edit :
All is good in your diskutil.
Thirst, it's better have a save Time Machine before doing the nexts steeps.
You can try 2 things :

List snapshots on your system :
tmutil listlocalsnapshots /


and il you see &quot;old&quot; snapshots you can suppress them and retry BootCamp
tmutil thinlocalsnapshots / 9999999999999 4


If no change, you can boot in Recovery Mode (cmd+r at boot time) and do a &quot;First Aid&quot; (as advised in the error window) on the System Container of the internal SSD. And then retry BootCamp after normal reboot.