We don't ask "make the longest palindrome". We ask "convert this English into code that does what it says". If you want to make the discussion more concrete, we have a public practice problem [1] that we send out with our interview bookings so that people know what to expect. The real problems we ask are very similar to it.

Do you feel like there's anything there that any reasonably skilled programmer shouldn't be able to figure out on the fly?

[1] https://www.otherbranch.com/shared/practice-coding-problem