I have similar problem atm. Udevil doesn't allow me to mount with compress=zstd:3 option. It's complain about udevil: denied 90: option 'compress=zstd:3' is not an allowed option
As I can see at /etc/udevil/udevil.conf there is no compress option allowed.
Is there a way to modify udevil.conf without recompile libreelec or modify squashfs?
Maybe add btrfs options to udevil.conf with PR?