I tried to run LE10 on the Pi4 I have. I downloaded the 10.0.2 image, unplugged my Pi3 running LE 9.2.8 from the AVR (Denon X2400h), and started it up. It seems to work fine except that I can't get CEC to work.
I tried in 1080p 30Hz, 60Hz, 4k 30Hz, 60Hz, no dice. Whenever I connect the Pi4 and LE10 through the AVR: no CEC. If I connect the Pi4 directly to the TV's ARC plug (Panasonic OLED TX-55FZ950), CEC works fine.
If I put the Pi3 on LE 9.2.8 back, CEC works fine. If I put LE 10.0.2 on that Pi3, CEC works fine.
The only combination that doesn't work is Pi4 on 10.0.2 through the AVR. Nothing else changes, all settings, cables, etc are the same.
Any ideas?