Pogba's role in the team is, or should be, to create chances and get forward to take shots, while also dictating tempo.
He has been creating chances for other players in matches, I'd say the only one to do so recently? He hasn't been able to get up the pitch though because of the paucity of quality around him, and he hasn't been able to dictate tempo because when he gets the ball all the other players run away from him! Often he is holding the ball, shielding it, because he recognises the lack of control other players have - such as Young's hoofball or Fred's giving the ball away - and recognises that he is going to have to shoulder the burden of United actually holding on to the ball.
Pogba so obviously wants to play possession football, and was so much obviously better when United started to do so when Ole first joined. Since then, United have moved to playing a more cautious, counter-attacking style, and with that lack of bravery on the ball from others, performances have fallen back to Mourinho levels. Pogba is then frustrated, because it means he has fewer touches, further from goal.
He's a top player, but unless the style changes back, or the personnel around him change, he's the wrong player at the wrong time for Man Utd.