Not really. A few of their developers have been redeveloping the menus. They redesigned the settings menu and it looks great. They're redesigning the content db pages and home pages. Some designs have been put out and I wouldn't be surprised if we saw something in the next few versions.
I don't think UI design is what foss is known for (outside of gnome)
? There's many more DEs (and not only) with beautiful design. Gnome is not something incredible here. And I can even argue about libadwaita being beautiful.
What would be cool is of they could make Minetest support third party launchers.
Why would you need that? What benefits outside of using other UI framework like GTK it can provide?
It's gradually getting there. The settings redesign was introduced a few versions ago, and the online content menu redesign will hopefully land in the next version (and potentially replace the current content tab after that). I agree that the main menu redesign might be a while away though.