I think his move to Chelsea reduced his playing form because the Sancho I knew that played in borrusia dortmund was an entirely different person as he was so in check with his playing style and also help the team in terms of goal but for now I think his form has greatly reduced and that deal is a really good deal indeed and who knows maybe he might get more playing time over there in Italy because that's what really going to help a player back in form.
Don't forget that he hasn't played for a long time since the problem with Ten Hag got hotter which made him lose momentum and was loaned out to Chelsea after a long time not playing obviously this requires further adaptation especially since he hasn't played for almost 2 seasons even though he is very fit but because the relationship is not too good at Manchester United, he has lost momentum for his performance.
Being at Chelsea or another club also definitely needs a new adaptation, it's just that when staying in the EPL it is clear that this is not something that Sancho can force to regain momentum.
Going to a competition where the tension and tempo are slower can be a good option and Serie A can be a suitable place for this. We can see Antony's form return after being in a competition that is a little slower in terms of tempo or maybe Greenwood can be an example and it can also happen for Sancho as long as he is serious about improving his performance in a new club.