Here's a good place to start. It isn't actual manufacturer's towing specs, which is the final guide for any vehicle, but it's a good list of what can be flat towed, taken from manufacturer's data.
Dinghy Guide If this is mostly a towing question,
I flat tow a 2016 Wrangler JKU Sahara that weighs around 4500lbs, loaded for travel (1/4 tank of gas), including all towing accessories, braking system, towbar, safety cables, wiring, et al.
Most Wranglers are easy to flat tow, partly because the steering doesn't lock, so no key in the ignition required.
Put transmission in Park, and transfer case in Neutral, and off you go.
My 2018 Navion weighs around 10,600lbs loaded for travel (full tanks diesel/propane, 1/3 water, empty black/gray) and including our "stuff".
Towing anything with motorhomes is more than just subtracting the GVWR from the GCWR. How much you can tow is simple math.
The weight of the "towed" can't exceed (3,500, 5,000, 7500 lbs) the maximum weight capacity of the hitch/towbar.
The total weight of motorhome + towed can't exceed the GCWR, which is 15,250lbs in my case.
So, for me 10,600lbs + 4,500lbs, and my total weight is 15,100lbs.
I have around 150lbs of buffer, which isn't much, but it's within the chassis specs.
I do my weighing just prior to departure, at a nearby MTO (government) Inspection Station scale.
Getting the weights done accurately is the most important part of towing.
After that, it's just simple math. You know your fixed limits, and just need to know the variables.