This is for those experiencing a similar issue on the Rock Pi 4B (possibly RK3399 in general) who don't have a fix yet.
On Armbian Focal current for the Rock Pi 4B the sound from both HDMI and the audio jack stopped working and became undetectable to the system (Both Pulse-audio and ALSA couldn't detect anything except hdmi-sound and even then HDMI sound did not work). I fixed the issue by rolling back to the latest "current" kernel version in armbian-config (5.10.63-rockchip64). Now the system sound has gone back to normal.
