edit I just figured out this article was posted 2 years ago on the Steam Deck community, personally I think is ok to repost because the game has improved a TON and it is worth checking up on! https://sopuli.xyz/post/10345987
This post is quite old and I think I am going to post a review of Luanti on the Steam Deck with a control scheme eventually, but I wanted to share this article in the mean time since I have been playing Luanti a lot on my Steam Deck lately.
Luanti is super easy to install on the Steam Deck, just go to desktop mode, open the "Discover" app, search for Luanti and click install. Done!
https://flathub.org/en/apps/org.luanti.luanti
Luanti also works great on Android from F-droid so if you are looking for a game and game engine that can be played on both a Steam Deck and an Android Phone Luanti is it!
https://f-droid.org/en/packages/net.minetest.minetest/
Something I want to stress, Luanti is a game engine that you can browse and download games from which are collections of mods. There are also mods that can be added to games.
One of the most popular games is Voxelibre, which creates an experience much like Minecraft.
https://content.luanti.org/packages/Wuzzy/mineclone2/
Nodeverse is worth checking out because it presents a game where you use a spaceship (like a flying boat kind of) to move around planets which are smaller instanced bits of land. You can then take off and explore other "planets" in the "solar system". This is a good example of how not every Luanti game needs to be an endless landscape with no constraints or macro form.
https://content.luanti.org/packages/aerkiaga/nodeverse/
However Luanti is a general singleplayer and multiplayer voxel game engine, so a wide variety of games can be made with the engine.
Take for example Build A City, it is fairly simple but the controls are there for a 3D management/rts type game.
https://content.luanti.org/packages/Splizard/buildacity/
Koboldkrieg also is an example of how a 3D tower defense game might work, again pretty barebones but it demonstrates that it is entirely possible in the engine.
https://content.luanti.org/packages/Nathan.S/kobo/
Also see Extra Ordinance a top down shoot em up.
https://content.luanti.org/packages/Sumianvoice/extra_ordinance/
I say all that to emphasize that don't look at Luanti and think this is just a Minecraft clone, it is really more like a Minecraft if it was open source and had a more generalist capability like Roblox to create different games.
There you go. Just publish it, and add a donation DLC that gives the user a badge, a mention in the credits or something like that.
Luanti is in the Discovery app which is the stock flatpak repository gui app "store" that comes with the Steam Deck.
No reason for it to be on Steam really, but I wouldn't be against it.
Steam is the largest game store ever. Why would they want to skip it?