I ssh into their machines that are available over a wireguard tunnel.
Android help is over vnc+scrcpy
To be honest this only covers 95% of the problems you could encounter so think about a pikvm[0] or something similar.
You can help them debug multiple PCs with one setup, you can help even when they lost their internet connection (hardware switch, driver problems - when nothing works use android usb tethering) You can even configure their bios/debug boot problems through this.