I don't quite understand your question either, since Redoinhunter has already answered it, but I'll try to clarify what the documentation says:
Please try not to upload just Steam keys, or put a link to your Steam store page without uploading any files. Someone buying a game on itch.io wants to be able to access it on itch.io through our website and app. If possible, your uploads should be DRM-free, but it isn't a requirement.
You can create a page on Itch that only has a link to the playdate page. Yes, the rules do NOT prohibit it (personally, I think it should be prohibited, but the rules don't explicitly prohibit it, only advise against it), but it's very likely that your page will NOT be indexed, since it doesn't offer any games within Itch.
Links to other platforms are intended to be a complement and NOT the main (and only) way to get the game.
For example, you can offer a game with achievements on Steam and a version without achievements on Itch. You create the page on Itch, upload the version without achievements to Itch, and include the Steam link in case someone wants to buy the version with achievements. The important thing is that you offer an option for people who want to buy and play directly from Itch without relying on another store.
Conversely, if your game doesn't offer this option and forces users to use another store, then you're not offering anything of value to Itch users. You'd only be using Itch to promote your game, and although the rules not prohibit it, it's likely that your page won't be indexed.