Just chiming in to make sure you attempted those repairs from a chroot environment, after booting the ISO; beyond that I’m no help with BTRFS.
Additionally, these links, though not specific to your issue, may contain useful information:
Cheers.
Edit:- I notice you have seemingly ignored the first of two links given. Trust that it wasn’t given randomly; the first link contains the procedure to mount BTRFS partitions for the purposes of chroot; in case this is needed. 