It seems to be a problem as the other partitions are formated in btrfs.
Perhaps a suggestion like mentioned in these threads could help but they are a few years old and I'm not familar with it. So please wait for an advice of an expert.
I also found that this symlinks should help (from LM forum 2025):
"#navigate to root of the partition with brtfs
cd /
#create symlink for boot
ln -s @/boot boot
#create symlink for etc
ln -s @/etc etc
#check if the links are working
#checks if the OS is detected and grub applies it
sudo os-prober && update-grub
"