I have had to revert to 10.0.0 as well because the CEC power on was happening extremely frequently with the same setup. RPi4 to Yamaha AVR to TV.
Hmm, probably we both see a behaviour which is not intended? On my side it's a Sony receiver.
Can somebody enlight us? 
Just to explain my usage of Libreelec:
It's installed on a Raspi 4. This one is connected via HDMI to a receiver and from there to the TV with HDMI too. Due to no comfortable solution to automatically shutdown and startup Libreelec I decided to keep it running all time.
This solution worked well with Libreelec 10.0.0 obviously due to a bug which was fixed in 10.0.1. The changelog speak about "powercyling related fixes for CEC".
Unfortunately this causes the bad behaviour that after switching off my TV and via CEC the receiver too Libreelec triggers the receiver to switch it on again.
So, my feature request is to bring back the bug of 10.0.0 as an option in case of Libreelec is not switched off. 
