The solution for https://discussion.fedoraproject.org/t/installer-crashes-when-btrfs-subvolume-gets-reformatted-while-having-nested-subvolumes/170252 calls for deleting subvolume var/lib/machines using the anaconda gui.
This fails for me on hardware using LUKS with:
ERROR: Could not statfs: No such file or directory Command ‘[‘btrfs’, ‘subvolume’, ‘delete’, ‘root/var/lib/machines’]’ returned non-zero exit status 1.
No log files in /tmp are updated during the delete.
sudo btrfs subvolume list /
[sudo] password for :
ID 256 gen 509335 top level 5 path home
ID 265 gen 509334 top level 5 path root
ID 266 gen 509317 top level 265 path var/lib/machines
(Deleting var/lib/machines worked for me in a VM w/o using LUKS.)