There is absolutely no evidence at all that Pogba is a hard worker on or off the pitch. It has nothing to do with his social media junk. There's no evidence he's a particularly hard worker in training, or that he looks after himself and his body like a Ronaldo or a Messi. He's underperformed massively for 2 years at United, with Mourinho shifting him into several different roles, trying to play defensive minded mids beside him, signing Matic, all to allow Pogba more freedom to go forward and not track back. He's one of the laziest CMs I've seen on the pitch. As evidenced by the ludicrous comparison he made of himself walking around the pitch to Messi walking around the pitch.
And no, Pogba was nowhere near as ridiculous and all over on social media at Juve as he has been at ManU, though part of that is likely taking control of his image rights, as iirc he didn't own them until the summer he left.
As a counterpoint, I always liked Pjanic at Roma and Lyon, but thought he was quite lazy and inconsistent. However, dude has worked his ass off since coming here, and turned into quite a defensively sound, hard working, responsible player (even if not perfect). He's also improved his fitness and stamina here. Pogba, since going to ManU has done the exact opposite.
So perhaps it's just environment, money gone to his head, being enabled. I don't know. Maybe a return to a no-nonsense club like Juventus/Bayern/whatever other top club would help him. Who knows. But if he doesn't get his attitude and mentality sorted, he's never going to be one of the best CMs in football, let alone the very best, which is what looked inevitable while at Juve.