I play on Fabric 1.20.1, and the absence of the "Mods" button on the main menu makes it impossible for me to actually know how to open the configuration menu

I'm also having the same issue. It seems like a bug atm with 1.20.1. Does anyone know any other configuration mods?

You will need to install a mod like Catalogue or Mod Menu to access configurations. Fabric doesn't have a mod list screen like Forge/NeoForge.