I know this is less than ideal, but what I did is I parsed a list of all android games from https://itch.io/games/platform-android and then created some ublock filters to highlight those titles in my library. Then I manually added all those titles to a collection which I can browse inside the app.
So I thought: since itch.io doesn't seem to currently be interested in maintaining this feature, and it seems really important for the purpose of this app, what if you used GitHub or something to maintain a periodically updated database of all Android titles on Itch.io, and then implemented a filter inside the app by matching the user's library entries against that database?