Recently itch.io added new platform filter for games -- "Phone browser". It seems like it checks if "Mobile friendly" option is set, rather than checking for input methods "Touchscreen" or "Smartphone".
If you choose the starting page filter option in the app to "...web, with touchscreen support" (and set "Popular" instead of "Top sellers"), you'll get ~10,000 games. But if you, instead, search for "Phone browser" games, you'll get ~100,000 games, which is 10x more to choose!
Looking forward to see this option in the app defaults picker.
Thanks for letting me know, I'll add that at some point.
For some reason this option is shown in the sidebar on Mitch app only for me, not on regular mobile and desktop browsers. So I'll leave the link here: https://itch.io/games/platform-mobile-web