No one is gonna search your game by name. Not a new game from an unknown developer. Itch will not promote your game (rare exceptions apply). Indexed or not. And your own promotion will include a direct link to the page. This link does not care, if the game in question is indexed or not, or if it contains a playable demo.
If you publish anything on Itch, it goes through a black box. The internals are secret. But it will have one of several results. There might be a delay, and a game can be put into that black box again, if you make an update.
1. Project gets "indexed". A few minutes after publishing it will appear when browsing on the browse pages with tags. It will also appear in ordering by date on the "newest" page. Also called "recent". If you publish and get indexed right away, of course you are on top of recent, because, well, your game is the most recent game.
2. Project gets on a pile of games for Itch staff to look at. As I said, specifics are secret, and maybe even 1 are quickly eyeballed by Staff. I do not know, I do not care, the result is what matter. Either you are indexed within minutes or it takes time. That time can be days, weeks, or over a month. Your game will not be put on top of recent by indexing date, but by publishing date. So if you have to wait 3 weeks, the game will be sorted among the 3 weeks old games.
Do not count on a boost in visibility by being on top of recent. It is pointless and if you release on Steam and have a webpage and whatnot, it will not matter anyway. Your goal is to be on new&popular and popular. The boost of recent is a few minutes of exposure.
3. Project gets quarantined. Same as 2. Staff has to check things and you have to wait.
4. Actually a result of 2 and said to be rare: the project will get intentionally not indexed or deindexed after previously being indexed. Failing to meet quality guidelines might be the reason for that.
5. Same as 4, but by automatic. Hard to tell if that happens or not.
Now. Publishing a devlog of the major update kind can get you on top of recent again. But those are staff approved. And staff will not approve most of those. As a rule of thumb, maybe 1 in 5 and every 2-3 months. If you publish and do a major update a month later, you are actually still on top of recent... just not on page 1.
Again with the exposure, being on Itch is passive. It will not do much. Especially if you have nothing to show. https://itch.io/docs/creators/quality-guidelines#avoid-only-uploading-keys-or-li...
Itch is not an advertisment platform. They expect you to sell the game here, not upload merely a demo version or a wallpaper. You do can include a steam key with the purchase. https://itch.io/games/steam-key
Does a game page with no downloads or playable files get added to “Most Recent”
A game gets indexed if it gets indexed. Sounds stupid and trivial, but that is what happens. And the recent sorting is simply a sorting by publishing date. Nothing more, nothing less. But some games will have gotten a timestamp bump by a major update.
Publishing date is not the same as on Steam. There is no such thing on Itch. Oh, you can make a page and set a release date, if you wish. Maybe to fulfill some publishing contracts or whatever. It will be displayed in the information box, and files and payments will be unavailable till then. But the publishing date is the date you hit the publish button or whatever it is called. Does not matter if your project is a prototype or a final game.
Will uploading a non-playable file (like a free wallpaper) satisfy the indexing requirement?
https://itch.io/docs/creators/quality-guidelines#do-not-use-unrelated-tags-or-cl...
Why is this a question? You did not upload a game. If it gets indexed, meh. Who cares. But technically you violate guidelines by publishing a wallpaper as a game. It is not a game. You can use a future release date, if you wish.
Does a game need to be indexed in order to show up in “Most Recent”?
Most recent is literally a list of all indexed games.
https://itch.io/games is the same list as https://itch.io/games/newest The only difference is the way it is sorted. Newest (called recent) is by date. Games is sorted by popularity. You want to be high on the popular lists. Like this one https://itch.io/games/tag-real-time-strategy