You wrote a comment implying what's wrong with Nix is the language, and stating that there's unfortunately "nothing better" out there.
It is true in this universe that there is a software project called GNU Guix, which is 13 years old, whose literal origin idea is - what if we take the general idea behind Nix, but write it all afresh in a fully featured programming language, and make it extensible and configurable with that language.
There are a host of reasons you might not want to get into that personally, as I stated - but it really does exist, regardless of your personal feelings?