Version 20.2? The latest stable version for Manjaro ARM is 20.12.
I got an “SD card not detected” message when trying to use btrfs for the boot partition. Some sources say the version 5.x kernel recognizes btrfs, but that wasn’t true for me. (When using vfat for the boot partition and btrfs for root, the message “btrfs is not recognized” came up when trying to mount root.)