I was on a trip today, just got back and I'll try to build newer kernel, possibly RT... Maybe I'll mess something, I don't know, this would be the first time for me to do something like this... Either way it's just another flash of SD card anyway... RPi4 works, fortunately...
I read something about issues with I2S DACs on Linux kernel forums yesterday, and there are definitely problems with the RPi5. Ubuntu uses kernel which doesn't include latest fixes for RPi5... I'll try to find links from browser history...