I have a Panasonic TV and CEC is fine on a Pi4.
Usually when there is a problem with CEC, you should disconnect all HDMI devices from the TV.
Unplug from mains for a few minutes. Power on TV and connect just the Pi4 through hdmi and power it on.
See if that simple setup works. If it does gradually connect other HDMI cables and check if any cause an issue.
If the simple case doesn't work, I'd be suspicious of the hdmi cable. Some cheaper cables don't actually wire up the CEC lines (or they could be faulty).
Also not all HDMI sockets on TV are the same. There may be some (perhaps labelled PC) that don't support CEC. Test with same socket that you've seen working on a Pi0.