We released our game here on Itch 2.5 weeks ago and the first week went pretty well for a downloadable cozy 3D adventure, but now the game is completely invisible. Despite having 5 stars with 23 ratings, games with only 1 rating and last updated in 2021 are ranked before us when searching for "Shoreline" (The game is called Project Shoreline). Are we perhaps breaking Itch's rules in some way? Is being shadowbanned a thing on Itch? We haven't received any form of notice of being banned or anything similar. I've also read the "getting indexed" topic and checked out settings. 

I would love any advice you could provide on how we can get some visibility again. We are working on an update but it would be lovely to have some visibility until then, right now we seem to be very invisible. 

If you mean silently lowering ranking and relevance for a game with shadowbanning, no, not to my knowledge.

The opposite is true. There is a hidden boost for new games that overinflates popularity. If that runs out, it might give a dropdown. Specifics are not talked about, but there is a thread somewhere that explained popularity ranking a bit and it boiled down to magic+boosts+whatever itch algorithm thinks that constitutes an interaction. 

The advice any admin or mod will give you is again and again, not to rely on being visible on itch as your marketing tool. You need to advertise elsewhere. Existing on itch is all nice and good, but why should people search you here or encounter you randomly? There is close to a million projects here. All want to be in the spotlight. 

Also, the current search algorithm in the search box is not really good. It searches mostly literally.

Your game is not named shoreline. It is named project shoreline. That is two words. The algorithm does not know that the second word is 100 times more important than the first word.

To give you an idea about your current "popularity" look at this https://itch.io/games/tag-3d/tag-cozy/tag-cute 

And I have no idea if search is ranked by popularity. It might have an influence. But I think it is mostly ranked by relevance. Or what the literal algorithm thinks is relevance. If it thinks you are relevant to a word, it will even find you with misspellings after the root of the word. And I seem to remember that search will first find exact title matches and fill up and probably cut off randomly less relevant partial matches.

(Oh, and updating might bump you to recent again. Please do not remove your game and reupload it. Some clever people try to game the system this way and it has bad consequences for everyone, including  those people)