I seem not to have right to re-open my previous topic so I am Continuing the discussion from Neither 'df' nor 'btrfs fi df' showing diff after deleting large files:
hm … despite the fact I have manually removed all copies of that file in all snapshots now I am not making any progress
$ sudo btrfs fi df /
Data, single: total=432.37GiB, used=432.37GiB
neither does $ sudo find / -name WS19.qcow2 return any remaining copy.