QGroundControl didn't connect

I am using SnapDragon for my flight controller
I followed this build instruction https://dev.px4.io/en/setup/building_px4.html

Everything was doing great. I was able to upload the firmware and run
./px4 mainapp.config
without any issues.

However, when I tried to connect it with QGroundControl, they didn’t connect to each other.
P.S. I connected my SnapDragon to PC via ADB and Serial Port

Does anyone know how to fix this?

You need mavlink streaming over the connection (serial or udp) to communicate with QGC.