You’re saying that other distros - like xubuntu desktop cannot even detect the Rockpi4 audio hardware. But then the ‘official Debian image for the Rock Pi’ does and the audio suddenly works fully ??
Hmmm… ROCK Pi 4 | No sound from 3.5mm jack · Issue #5941 · MichaIng/DietPi · GitHub
DietPi is a lightweight Debian. And it is not detecting the audio hardware on the RockPi4 either. Maybe there’s some driver in the Debian image that can be added from Debian into DietPi…
IDK 