Greeting!
I’ve just successfully used ELRS-MAVLink for telemetry. It’s quite simple MAVLink - ExpressLRS can be helpful.
Note that both the Tx and Rx should be running ELRS version >3.5. After updating, you can simply modify a few parameters of PX4 in QGC, and everything should work.
Good luck!
I’m also looking for solutions for OSD because I couldn’t get my Avatar HD to work with PX4 (no OSD information on the screen, although the msp_osd status seems fine).