My understanding is that 4WD isn't towable on a dolly.
That's not universally true. Generally, AWD (All-Wheel-Drive) cannot be dolly towed, but AWD is technically different than 4WD in that it lacks a shiftable transfer case. 4WD that has a transfer case with a selectable neutral can be dolly towed (in 4WD neutral). However, some 4WD have elecronic shifting that lacks a neutral and those too cannot be towed in most cases, dolly or flat.
Also be aware that all 2WD are not dolly-towable. Most rear drive 2WD these days cannot be dolly towed for the same reason they cannot be flat-towed - lack of transmission lubrication & cooling.
With so many different drive train types these days, about the only useful advice is "check the owner manual", usually under Recreational Towing or simply Towing.