Yes, to get the telemetry data to the GCS over wifi you need MAVLink, and to get the Yaapu script to work you need CRSF.
Notice pretty much ever part of this is either Dev, Alpha, or Beta firmware. So I wouldn’t throw this onto anything of significance or value.
Arducopter 4.1.0Dev
Yaapu 1.9.3 beta4
Matek F405-Std
CRSF 4.11(beta) (Wifi 1.41Alpha)
Radiomaster TX16s (OpenTX 2.3.11)
NanoRX Output 1&2 Mavlink TX/RX. Output 3&4 CRSF RX/TX.
On the FC
CRSF on TX3/RX3 (Serial 1), SERIAL1_PROTOCOL = 23 (Baud 57)
MAVLink on TX4/RX4 (Serial2). SERIAL2_PROTOCOL = 2 (baud 57)
I’m sure there’s something else I need to tell you but I can’t think of it right now. If it comes to me I’ll let you know.
Good luck!
Edit: Here’s all the info on setting up Yaapu. Maybe start from the end, it’s a long thread and has evolved a lot.