I have a 2020 Touring XT and did exactly what you are proposing. I replaced the factory tires and the donut with Falken Wildpeak A/T Trails in the factory size of 225 60 R18. There is absolutely no problem putting a fill size spare tire in the spare well in the Touring. It’s the same well in the Onyx. But, the rectangular foam insert that goes over the donut in the Touring and holds the jack, etc., will no longer fit with the full size spare. I and some others have purchased the smaller circular foam insert for the Onyx which is designed to work with a full size spare. Others just forego the foam altogether and use the extra space for storage.
I didn’t put a tire pressure monitor in my spare, but you can put one in there and have your tire installer program the TPMS to recognize it and the Touring will then recognize the spare if you ever mount it and give you accurate tire pressure readings.
