CEC itself yes, but maybe "turn on by CEC signal" isn't? My TV has this option and it works with OPi 3.
I have an LG TV I think it supported power on via CEC. It worked with libreelec on RPi 3, I will try that again. However, that ist not my actual problem. The problem is the following:
The screen stays black if Libreelec (OPi H6) boots without TV turned on. So I need to manually turn on the TV before booting Libreelec, otherwise I have a black screen. The HDMI connection, however, does seem to work to some degree because even when the screen is black using the remote control I can hear the typical Kodi sounds via the TV.