[SwissXC90]

At the rear of the XC90 is a plastic roof panel

On the earlier XC90s, the AM and FM and TV antennas were installed under the roof panel

On the later XC90s, such as your 2010 XC90, the AM and FM antennas are on the rear most side windows. But the roof mounted plastic panel still exists.

I would recommend mounting the antenna under the roof plastic panel so that it is out of the weather and cannot be seen.

Run the antenna cable from the radio up the A-pillar, tuck it under the roof lining to the rear of the vehicle.
You can access the rear of the vehicle by pulling down the rear roof panel from the inside. You have to remove the side panels first.

Very important for good DAB reception is a solid ground connection to the body of the car, so use one of the various bodywork bolts you'll find under the panel to connect the antenna ground.