A project is a promise to be the thing. Not an advertisement of the thing. You list the project in the game category, after all.
That's why I think demos are borderline. At least Itch users can download and play something. Also, the full game might be released to Itch at some point.
But merely uploading a project to have a project page that links to another store? Seriously? That is a blog post in disguise. You can make actual blog posts here. Consider doing this, if you cannot even upload a demo version of your game.
In case you missed it, if your project will not have any files, it almost certainly will not be listed at all in the index. And rightly so. Why list a non game in the game category. And if your project does not have any files, it is not a game, it is an advertising page. Itch is not a catalogue of games like for example https://www.mobygames.com/ .