Hey there!
Recently I decided to delete gnome-boxes to try a different alternitive and when I uninstalled it the boxes VM’S and all its attachments didnt get deleted so the not used vms take alot of space on my system.
Solutions I tried:
Installing again to see if the boxes were there and delete them manually. (they werent)
sudo apt-get purge --auto-remove gnome-boxes
sudo apt-get purge gnome-boxes
sudo apt-get remove --auto-remove gnome-boxes
sudo apt purge gnome-boxes