Behavior is identical in 10.1. What you could do, without rebooting: open another shell (ctrl-alt f2), luksClose the crypted volume, pgremove the physical volume group, then comes the scary part: add some amnesia to partman. I did a # mv /var/lib/partman/devices/=dev\=nvme0n1 /tmp/, went back to the installer and could re-do whatever I wanted to do.