I don't know, I just use FDE because I don't trust filesystem level encryption to protect against the many side channel attacks one can inject into a running system. LUKS is good enough for me.

It looks like there's slow but steady progress on FSCRYPT support on BTRFS: https://bkhome.org/news/202403/linux-kernel-btrfs-supports-f... No idea what kind of state it is in currently.

The latter at this point.