All other icons, other than the folder icons are from respective app developers, Gnome or otherwise, which could either be left alone as is, or placed over a background. You, @c-lobrano know how to do that. The background doesn’t do anything to the icon, and the background is what that differentiate Ubuntu from other distros.
There’s only 14 icons as folder icons in Yaru, and they can be Ubuntu specific, without any copy of others’.