Meta Transferring Teams

I would highly encourage you NOT to worry about this at all.

What team you join as a full-time is a "later" problem -- the problem at hand is to do really well in your internship, regardless of the team. If your manager, teammates, and the company like you enough as an intern, they'll bend over backward to ensure you're happy on the team you want to join as a full-timer.

I don't have numbers on this, but I think most interns do not return to the team they interned with (I think none of the ~5 interns I directly worked with returned to Instagram Ads). This is because interns don't get to choose their teams, so they often look for greener pastures after the internship.

This means that returning interns will go through the bootcamp system. However, things have changed since the big layoffs. Bootcamp as an institution is unfortunately dying, so it's possible that interns are more heavily pushed towards their intern teams now. I would ask your intern manager about this after you start.

In the meantime, make sure you nail the return offer, which is something you want to do regardless of how team selection works for returning interns: [Course] Nail Your Return Offer As A Meta Software Engineer Intern

I also wouldn't worry too much about the space a team is in as the team choice shouldn't matter too much for junior -> mid-level promotion. For Meta in particular, your goal after joining is to grow from E3 -> E4 as fast as possible to make yourself more attractive to more teams and survive up-or-out. You can learn more from the L3 -> L4 course here: [Course] Grow From Junior To Mid-Level Engineer: L3 To L4