Elixir is often presented as "done" (https://elixirforum.com/t/is-elixir-done/20830/12). For example, the depreciation policy mention that function can only be removed on a major version (1.X to 2.Y for example), and for now it's still in 1.X and no Elixir 2 is planned.

It still has releases (https://elixir-lang.org/blog/2021/05/19/elixir-v1-12-0-relea...) to follow Erlang releases, but Erlang itself is also more conservative than some other languages.

It's hard to imagine that a language can be "done" when the problems being solved with it keep changing and we keep discovering new techniques for solving them.

When is automotive design done? Farming?

Features that you don't use carry a cognitive load, increase the number of choices you have to make, and reduce the usability of other features that they have to be disambiguated with.