How did you open this? Maybe something overrode your default text editor application (look in settings for Default Applications).
Also maybe check your EDITOR env variable (echo $EDITOR), though that is only used when a different CLI program wants to open an editor for you (in CLI)

You are replacing partitions with subvolumes, as such you have to make these operations on the btrfs filesystem (so as others have already written, deleting the subvolume instead of re-formatting the partition).

Did you try containers? Though truth be told I am not amazed by any of these solutions too.