I have pushed a new possible fix for all this stuff

They said:

If you’re using the compile-package API it does not because it cannot tell all the beam modules until after they are compiled, but that’s not the job of Gleam in that case.

And I can’t just create a minimal one because

It would be incorrect if there are Elixir modules in the package

I think once files are compiled there is probably something in mix I can use to generate the .app file? I can then inject Erlang options from gleam.toml

The Gleam compiler only generates Erlang from Gleam modules, but it doesn’t know what any Elixir modules in the package expand to, so it cannot create .app files unless it owns the whole project and so will be performing Elixir and Erlang compilation. This means that any build tool that uses the Gleam compiler will need to generate the required BEAM .beam and .app files.

edit: Oops, I saw Papipo beat me to it!