First post, but I have experience with this issue on my GRX double front chain ring, and determined that the best way to remove and replace the rear with the clutch derailleur is to move the rear clutch to the off position, all the way down,
switch to the small ring in the front; move the chain to the middle of the rear cassette and then pull the rear derailleur back by pulling on the jockey wheel on the rear derailleur and let the guide the chain off the cassette. It will still be tight when compared to a road bike, but easier than having the front chain ring in the big ring
When replacing the rear wheel, switch to the small front ring and middle of the rear cassette. and put chain on the middle rear cassette that way the rear disc brake has enough space to fall back into the rear caliper.
Hope this helps and once you figure it out, it’ll be easier the next time.