The rear wheel of the volvo ex90 won't come off the car even with the lug nuts off. is there a trick to this

Most likely its rusted to the hub. Grab some PB Blaster and a sludge hammer. Spray the middle of the wheel the best you can and then tap the tires sidewall at the 12, 3, 6, 9 positions and treads with the hammer. It should break free after a couple of taps.