[RPi5] Remote/CEC not working with TCL TV running ROKU

I have a TCL TV running ROKU. I can't control my Raspberry Pi 5 with my remote.

I fixed this by following the following steps:

1. Quickly press the following on the TV remote: Home x5 > Rewind > Down > Fast Forward > Down > Rewind.
2. This will open up a secret menu, "TV Secret Screen", where you should enable "CEC Remote Control".
3. Turn the TV off and on again, it should now work.

I am documenting this for posterity.

A useful command for debugging CEC is cec-ctl --monitor.