Okay, so, the steps are:
- connect your SBUS receiver to the DSM/SBUS RC port of the PixHawk4
- set your receiver to SBUS mode (depends on the receiver, for X8R you have to put the jumper on the right position, check the documentation of the manufacturer)
- make sure the receiver is properly bound to your RC transmitter
- start the calibration again in QGC, make sure the RC is not too close to the receiver
Try to reboot both the drone and the transmitter if not working.
You can also connect the receiver to a SBUS analyzer if needed.