LibreELEC 11 has aarch64 kernel but arm (32bit) userspace so you can't use aarch64 docker containers, you need to use arm (32bit) containers.
LibreELEC 12 (development just started this week) switched RPi4 to aarch64 - but it will take a while until it's out and as it's bleeding new edge right now I wouldn't recommend switching to it unless you are prepared for a bumpy ride, constant breakage and lots of bugs.
so long,
Hias