I do not understand the question.
You asked if this is frowned upon and you claimed to have read the docs and did not find it.
Yes, it is frowned upon. It is even completely pointless. Itch is not a homepage service to host a game's advertisement page, but not the game files.
There is no app store facility on Itch. You can't install games on a device by a store app. Yes, there is an Itch app, but that is just for desktop computers and basically is just a custom browser. I am not aware of any games that need the Itch app. Maybe some home brew drm or whatever. So in terms of sideloading, all games on Itch are sideloaded. And there are only some external stores that are supported with an "official" link in the meta data. Unsupported external links just have to select "other".
Playdate games are here. Just look how they do it. It's 1500 games.