I'm a huge fan of strongly typed functional programming as it seems to help me produce more robust applications.
Though honestly I can’t really recommend any functional language stacks beyond that. I use Haskell/Elm stacks a lot but I regard Haskell’s backend development APIs as … immature. Stable effective but batteries aren’t included and you’ll often have to write those. I don’t usually need much out of my backends so it usually suffices but ymmv.
Scala’s got it better here but the tooling is tiresome to work with, though the community making strides. I can’t say much about Clojure’s options but it’s not strongly typed anyway. Still you could easily rock a JVM stack functionally.
If Elm is your jam there are some active/upcoming backend solutions coming out of that community like Lamdera and Roc.
PureScript isn’t any worse a choice than Haskell, has more effective JS targeting and good integration with the NodeJS ecosystem. It can serve as your full stack, though I can’t speak to its efficacy/maturity as I’m only passingly familiar with its ecosystem.
I’ve never investigated OCaml’s ecosystem but it could be worth a look. It’s been having a moment, though not exactly in web stuff.