For Elixir specifically, I liked Dave Thomas’ Elixir for Programmers. https://codestool.coding-gnome.com/courses/elixir-for-progra...

For learning about performance and low level stuff, Casey Muratori’s Performance Aware Programming course has been great. https://computerenhance.com

For higher level software design stuff (beyond just GoF patterns), check out James Koppel’s writing at https://www.pathsensitive.com/ and his courses at https://mirdin.com