I've been using user friendly distros for some time (opensuse, fedora, manjaro, ubuntu). I just downloaded Garuda since it sounds like what I want a fast distro optimized for games. I would like to install Budgie desktop, and use it alternating with KDE. When I just want to relax and need things to be fast, I'd use Budgie.
I've never done that, so I don't know if there's some special way of going about it, or just install the budgie package.
sudo pacman -S budgie-desktop
with this command, you will be able to install all necessary packages for budgie. And also Xorg is necessary but as you'll be using both KDE and Budgie, so, Xorg will be there.
Installing multiple desktops is not supported with Garuda as there can be many unforeseen negative side effects by doing so. You are on your own for support if you do this.
The instructions above are far from the safest method of accomplishing this. At the minimum you should install a different desktop to a different user account. The safer method would be to install the other DE to a different partition and dual boot.
The method you marked as the solution is neither recommended nor supported by Garuda as it generally cause conflicts between config files with many DE's.