Don’t believe that Sané really wants to go to the Premier League again. The most I could imagine is that he doesn’t like the reporting and focus at Bayern that much. At Liverpool he might not necessarily have to take on the leadership role that is expected of him in Munich.
Ultimately, I think he’s just using a possible change to negotiate out a few more euros, as is usual (disgustingly so). Of course, it helps if you can get as concrete an interest as possible from another club.