Alright so this whole Boba Fett spinoff series is still a massive rumor at this point, so please take this latest update with a grain of salt, but it’s sounding like if this project is legit, it will be a prequel to The Mandalorian, and not directly set during it.
This update comes from The Direct, which is also claiming that Sophie Thatcher is attached, and that Jordan Bolger is in talks to star in it. Both are described as supporting cast members, so the focus would still be on Boba.
If it is a prequel, then one would have to think it would all be set on Tatooine, and that it would at least explain his Sarlacc escape, and how he ended up hanging out in the Dune Sea like a nomad. If Bolger and Thatcher are attached, then one would have to think that they may assist the Bounty Hunter after his escape, but who the hell really knows at this point.
Like I said this is all “Wild Rumor” territory at best for now, so stay tuned for more details if they become available.