I agree the clutch is probably suspect. To confirm , try a couple different things.
Shift into 4Hi and repeat the tests to see if it moves or if it’s still possible to shift with the clutch engaged. Do it again in 4Low. That should rule out transfer case issues.
Try shifting into the top gear from neutral with the clutch engaged and the engine running. Take note if it goes in right away or if there is a pause (due to the synchro speeding the assembly up). If there is no pause (same as if the engine were off), then that means the shafts aren’t spinning, and the issue is forward of the input shaft.
If there is a pause, it is possible there is an issue downstream.
