Writing dotfiles into the root of user's home dir is not really a thing anymore.

For linux, there's the XDG base directory specification. This would make the location by default something like ~/.config/aider/config.yml. See https://gist.github.com/roalcantara/107ba66dfa3b9d023ac9329e639bc58c#file-xdg-cheat-sheet-md

On a mac ~/.config is probably better for a terminal app than going to the "correct" ~/Library/Application Support/aider/config.yaml. Tools like git, github copilot, gh cli, shells, neovim and many others use it or at least will make a symlink from there to Library.

On windows %APPDATA%\Aider\config.yaml is probably good.