MRudolph the EDID contains the physical HDMI port address so if you switch to a different TV or even to another HDMI port on your TV that'll easily break CEC if you ran "getedid create" before.
But since your RPi4 seems to detect the old TV fine you could use that to grab the EDID of your old TV and then use it on your RPi5:
Start LE12 on your RPi4 with HDMI-A-1 connected to the HDMI port of your TV which you'll then use for your RPi5.
First make sure you have no edid override in place, if in doubt run "getedid delete" and reboot so the RPi will actually read the EDID from the TV.
Now ssh in and run "getedid create" to grab the edid, you'll then have a edid-HDMI-A-1.bin file in /storage/.config/firmware/edid/ which you need to copy over to your RPi5.
On the RPi5 make sure you have an edid override (from getedid create) in place, the one from your new TV will do fine, then overwrite the /storage/.config/firmware/edid/edid-HDMI-A-1.bin file with the one from your RPi4 and run "create-edid-cpio" to also update the initrd (which contains the edid firmware override for early stage boot).
Now the RPi5 will have the correct edid of your old TV and hopefully CEC might work better - you may need to wipe CEC settings in kodi, it could also still have physical address overrides and then things go south.
But CEC is a bit of a mess, every TV vendor seems to implement it differently, so it could also be that you'll still need to switch TV inputs to get it working.
so long,
Hias