Herelink uav3

I want to use herelink for my UAV 3 project, but I want to connect an external button and joystick to herelink, is this possible and is the number of communication channels supported? if possible up to how many channels it supports

It’s possible but right now it’s not enabled in the Herelink ground station versions of QGC. You’ll have to use a second device (Android or Windows tablet for example) as a companion computer.