Just put a # in front of the line in armbian.list (should have the same effect as freeze kernel in armbian-config):
cat /etc/apt/sources.list.d/armbian.list
# deb http://apt.armbian.com bullseye main bullseye-utils bullseye-desktop
Regarding a new kernel: the new ones (newer than 5.10.43) do not support emmc speed HS400, seem to have issues with the 2.5Gb/s interface (transfer rates are about half the speed), and the switch to the new mainlined bootloader is essentially untested... Would be wise to focus on this - besides the general stability.