Dear Werner,
I recently installed Armbian 25.2.3 KDE Neon with vendor kernel 6.1.99 on OPi 5 Plus, and the sound does not work either. It apparently has something to do with the kernel version: switching to 6.1.75 solves the problem. Going to the higher vendor kernel version causes the problem to reappear. Is there a fix for 6.1.99?