Coaches and teammates can help the adaptation process of a new player. If his new teammates don't like the new players, then they must be having a hard time in their new team. Lionel Messi is also having trouble getting his best form at PSG, that's also because his team-mates don't support his adaptation 100%.
It will be unfair that a club will still expect Messi's best form when everyone knows he has played well past his prime, and although he can still be significant in games, he can not be as good as he was when he played in Barcelona where he had his best form. He did not settle in in PSG because of what he complained about which was the club supporters. Messi for any team that signs him now will be a figure and not be as good as before, he will be signed because of the name he already has in the sport.