> If you want a language where const is the default and mutable is a keyword, try F# for starters. I switched and never looked back.

Rust is also like this (let x = 5; / let mut x = 5;).

Or you can also use javascript, typescript and zig like this. Just default to declaring variables with const instead of let / var.

Or swift, which has let (const) vs var (mutable).

FP got there first, but you don't need to use F# to have variables default to constants. Just use almost any language newer than C++.