What I ended up doing for NanoPC T4 is disable the systemd service and in rc.local:
/usr/bin/brcm_patchram_plus_rk3399 --enable_hci --no2bytes \
--use_baudrate_for_download --tosleep 200000 --baudrate 1500000 \
--enable_lpm --patchram /lib/firmware/brcm/BCM4345C5.hcd /dev/ttyS0 &
> ... bluetooth doesn't work and I've got a flood in Rock Pi 4 syslog
The --enable_lpm stops the flood and allows it to more-or-less complete.
FWIW I haven't yet seen an Armbian 5.x kernel where both wifi and bluetooth actually worked on the T4, but I haven't tried 5.x since I started messing around with brcm_patchram so maybe ...