Standard advice for a jammed 4x4 SUV is to drive backwards making S-curves, to unwind the the tension in the driveline.
If that won't do it, jack up one front corner to release the tension.
Or even lift front and rear tires on the same side, block the tires on the opposite side, then run it in gear (slowly!!!) for a moment, forward and reverse, while tugging on the lever. Assuming the diff lock isn't engaged, the lifted tires should turn without turning the side that is still on the ground. Think safety, don't do this where leaping off the jacks could hurt anything.
Beyond that, it might be broken parts.
Tell us how this turns out!