After even more reading, i came to a conclusion that my external telemetry radio is actually most likely connected to Serial 4 port, because the solder pads on the board say “R4” and “T4” which, I think, correspond to Serial 4. After changing SERIAL4_PROTOCOL to 1 (MavLink 1) or 2 (MavLink 2) On Mission Planner via USB, I still can’t connect to the board via Telemetry, am I missing something?
Also sorry for all the mistakes I make, I can fairly say that I’m still pretty new to these new devices, I didn’t need to setup these Serial ports on APM, so I don’t really know how to do it.