There are too many out-of-date guides about configuring emacs for elixir with too many options, etc. so I wrote yet another one for anyone else already running at least emacs 30.1 (with built-in elixir-ts-mode) on macOS (with home-brew) and prefer eglot over lsp:
https://blog.digressed.net/2025-09-30-emacs-30-1-elixir.html