It looks like itch.io doesn’t provide platform information anymore for the library. It used to be hidden within https://itch.io/my-purchases, there was some unused HTML for displaying Android, Windows, Linux etc icons, and I relied on that hidden HTML for filtering. But it looks like it has been removed now (and the way they load thumbnails has changed so that’s broken too).
Thumbnails are an easy fix but sadly the Android filter will be much harder or even impossible to fix.