Which kernel are you using? linux-aarch64 or linux-raspberrypi4? I will say that in comparing the config from linux-raspberrypi4 (aarch64) to that of linux-raspberrypi4 (armv7h), I do have them configured differently for BTRFS (mistake on my part which could account for the difference.
$this->bbcode_second_pass_code('', '% grep -i btrfs core/linux-raspberrypi4/config8
CONFIG_BTRFS_FS=m
CONFIG_BTRFS_FS_POSIX_ACL=y
# CONFIG_BTRFS_FS_CHECK_INTEGRITY is not set
# CONFIG_BTRFS_FS_RUN_SANITY_TESTS is not set
# CONFIG_BTRFS_DEBUG is not set
# CONFIG_BTRFS_ASSERT is not set
# CONFIG_BTRFS_FS_REF_VERIFY is not set
% grep -i btrfs core/linux-raspberrypi4/config
CONFIG_BTRFS_FS=y
CONFIG_BTRFS_FS_POSIX_ACL=y
# CONFIG_BTRFS_FS_CHECK_INTEGRITY is not set
# CONFIG_BTRFS_FS_RUN_SANITY_TESTS is not set
# CONFIG_BTRFS_DEBUG is not set
# CONFIG_BTRFS_ASSERT is not set
# CONFIG_BTRFS_FS_REF_VERIFY is not set
')
I just pushed
46798bd3fc which corrects that. You can try updating via a chroot to that kernel when it hits the repos and see if it boots for you. If you remember having the ability on armv7h then the bootloader can do it and aarch64 should be consistent.