I agree. I've been trying to learn functional programming for years. My brain just doesn't get it. And I've actually built a non-trivial web app in Elm, and started trying to write one in Gleam and I was very very slow and unproductive. Eventually I gave up and wrote the whole thing in Go + TS for the frontend.
For Gleam I was trying to write the whole FE + BE in the same language - I really like that it can be compiled to JS, and I'm honestly sick of the whole React + seven thousand dependencies game, so I was using Lustre (an Elm-like library for Gleam). And again, I've programmed an app in Elm, after a lot of hair pulling, and in the end I didn't enjoy it that much.
I've gone through tutorials and I don't understand things like types having different wildly unrelated constructors, currying (I didn't notice much currying in Gleam but really disliked it in Elm, I cannot follow past the first or second arrow). For writing the front end of the app, I would make _zero_ progress unless referring to other Github projects (and it was hard to find any since Gleam was so new). Anyway, if someone has a book or something that can teach me this stuff it would be great. I want to use the OTP and a single language for FE/BE that's not JS. I'm not dumb, I've been programming since I was a little kid, but maybe I'm too stuck in imperative models.