How often do EMs and TPMs go from this role back to a senior IC role?

To go back to IC from EM, this implies that you moved from IC to EM. This means that those going back must be a subset of those that moved in the first place, so it has to be more common to take the first step.

With that said, I think this is too situational to generalize. If the roles pay about the same, and both have upward mobility (career track for both), then switching back would be far more appealing (and possible). I know quite a few people who have managed people and don’t any more. I am on that list.

Regarding more senior level folks… I imagine most more junior folks aren’t in a position to be moving to a people management role, and I think the jobs overlap more and more the higher you move.

EM -> Senior/Staff engineer is fairly common (EM is an entirely different job and many tech leads realize they can't do that job after switching). My 1st manager at Instagram was forced to transition back to E6 (Staff Engineer).

TPM -> IC engineer is very rare (I actually don't think I've seen it happen ever). Many TPMs ironically don't have technical backgrounds and are more generalists with decent business skills.

IC -> TPM I've seen a couple times too.

Do all the interviews at FAANGMULA companies for ML engineer roles require really basic DSA from like college vs ML specific questions? In my experience (non-FAANGMULA companies) with data science they end up being more an analyst or ML type of specific questions than the ones I had in college (binary search etc.). Some places still do the standard DSA from college though.