You can always take the easy way out and just symlink stuff. This is what I actually prefer. Then I can edit those files in their native format and just check the updates into my .config/home-manager git repo

    home.file.".gitconfig".source = config.lib.file.mkOutOfStoreSymlink ./dotfiles/git/.gitconfig;
    xdg.configFile."nvim" = {
        recursive = true;
        source = config.lib.file.mkOutOfStoreSymlink ./dotfiles/nvim;
    };