I just installed Armbian 5.88 for Rock Pi 4B and bluetooth is not working. I'm using ARMBIAN 5.88 stable Debian GNU/Linux 9 (stretch) 4.4.180-rockchip64 Do you need further information? Got it working without compiling the new kernel. i manually ran the last steps of https://github.com/armbian/build/blob/master/config/sources/rockchip64.conf and copied rk3399-bluetooth.service and brcm_patchram_plus_rk3399 onto the device and set up the service... after a reboot Bluetooth is working fine. Thats great!