If it’s any consolation, we are trying to address this to make it easier. Unfortunately Silverblue (the upstream) doesn’t really like doing dual booting either.
How have you felt the Ally? Have you had burning SD issues? I want to try the bloody thing, but every shop that has it, the games just ain't working or if they work, they are crappy games I'm not interested to play at like FIFA
Couldn't you first make a Gparted Live USB, boot it up, do all the partitions, then create back the Bazzite/Silverblue USB, and just mount those new partitions?