LG tv same problem.
RPI 2 & 3 - CEC works for years, RPI4 not working.
Thanks for fix.
Sorry, I was to fast with posting.
After googling in some other forums, I have found, that for CEC to work, HDMI must be plugged to the port next to the usb-c/charging port. Moving the HDMI cable from the other HDMI port to this one helped and now the CEC is working as well.
Might be a good tip for someone new as me