I'd like to add a new gallery for UI widgets see extension https://extensions.libreoffice.org/extensions/gui-widget-prototyping
there are two galleries one has widget and the second one icons. Both can be used for UI related stuff.
Please share an image here so we don't need to install extensions.
Created attachment 158735 [details]
Created attachment 158736 [details]
My first impression: too many items, not ultimately relevant for an office suite (although some people report this use case). So my take: extension.
OTOH, if we get rid of the pointless "Computer" gallery this one makes a bit more sense. See also bug 131308.