I would try on dirt or grass but with the hubs locked. No expert on Ford transfer cases but similar to the Jeep’s. The shifter is moving one or more rings causing multiple gears to lock up to each other. So when you free wheel (Hubs unlocked) the other half of the system will just go along for the ride. When they both have resistance they have a bit of a tug of war and may separate or push the locking ring or other device out of the way. If your selector has resistance and seems to click between 4l, 4h, and 2wd then likely it’s just stuck in between and locking the hubs can help undo it.
You could have a damage fork or gear, in that case off it comes for repair.
Some other members will weigh in shortly.