Without get agreement both side between Pogba and Manchester United next window transfer opening Pogba become free transfer player and all club looks easy to get his sign's,
I think that's what Pogba wants. If he were on a free transfer, he could demand a much higher hand money in contract negotiations with his new club. It was similar with David Alaba, for example. He had rejected contract offers from Bayern again and again for a long time and gained time until Bayern could no longer sell him with a transfer fee. In the end, he moved to Real Madrid last season without a transfer fee and got a big hand money from his new employer.
I think this is quite reasonable because even though Pogba's abilities are not like when he was at Juventus but he is still one of the players who are quite in demand but until now he has never wanted to go anywhere despite rumors of him with Juventus and Real Madrid. on the other hand he also refused a contract extension on the grounds of salary.
I think this is a strategy that Pogba wants to do because it is certain that when he is free, he will automatically get quite a lot of money later.