You can definitely put all of your configuration into a single file for AstroNvim if you want.

In the docs it shows the minimal configuration to get AstroNvim running which is <10 lines in your ~/.config/init.lua file and then anything else you can just drop in that same file if you want. (https://github.com/AstroNvim/AstroNvim?tab=readme-ov-file#mi...)

Here is a user on GitHub that has a single file AstroNvim configuration: https://github.com/20k-ultra/dotfiles/blob/master/nvim/init....