I'm actually dual-booting both systems on my laptop ie (Funtoo's kernel and initramfs are on the same EFI system partition that Windows uses)
Admittedly, I configured Windows to mount those Btrfs partitions at startup, and for both OSes to be able to hibernate, so that I can access the affected partition by hibernating one OS then resuming on the other. This worked well for about three weeks.
Anyway, are there commands to try to recover /dev/nvme0n1p{6,8}?