[SwissXC90]

Easy

Get the wiring diagram for your model Volvo.
if the exact MY is not available, a year before or after doesn't matter. As long as the diagram is pre-facelift or post-facelift to match your car.

Look at the LIN bus wiring from the SWM
See what connectors it goes to
Measure resistance of LIN bus to ground with everything connected.
If VIDA is correct, it will be 0 ohms to ground (of something close to 0)
Then start disconnecting the connectors until you have isolated the fault

Example of MY2009 XC90:
The CEM connects directly to the SWM via LIN
The SWM connects to the Clockspring via LIN
The Clockspring connects to the Left buttons and the Right buttons via LIN

In electronics repair there is a saying: "if it moves, it breaks"
Thus suspect #1 is always the Clockspring.

Unplug the Clockspring from the SWM and see if the short disappears
If so, plug it back in, and then unplug the buttons in the steering wheel and see if the short disappears
If so, the Clockspring is the culprit