The definition of computation depends on the abstraction level. Languages span multiple abstraction levels. The point is that there’s no meaningful definition of “declarative language” as proven by the examples I’ve already given.
For example you can “compute” a roguelike in TypeScript types, but a type system is declarative!
If you are willing to go to extraordinary lengths, then yes any programming language can be written in a declarative style, at least some part of the program. Some parts of a Java or PHP program can be written declaratively.
In the Nix language context however, they mean declarative and functional like Prolog.
There is also Guix which uses Scheme to declare dependencies, and Scheme is not a declarative language. Scheme is a functional language, but it can be easily written in a declarative style.
For example you can “compute” a roguelike in TypeScript types, but a type system is declarative!