According to: CRSF Telemetry (TBS Crossfire Telemetry) | PX4 Guide (main)
CRSF is not available in firmware releases; you need to build custom firmware in order to use it. Then, you have to set 2 parameters that are added in the custom firmware (not available in releases).
So does that make RC_PORT_CONFIG + RC_INPUT_PROTO == CRSF useless?