I agree with silerhelm and DaveT. Shot hub spline, shot CV joint or not properly engaged in 2wd mode.
All are easy to investigate and relatively cheap to fix too, unless your 2wd setting within the gearbox is shot, but you’d have metal chunks in the gearbox oil if this were the case - and it would be the last thing I’d check if you don’t find any other issues that resolve the problem.
Cheers
Bennie