This is a feature I have always missed in Łowcygier.pl - being able to only display games available natively on Linux (or another OS for this matter). I can see that platform information is easily accessible eg via the Steam API (say, for Factorio: https://store.steampowered.com/api/appdetails/?appids=427520), so I believe it shouldn't be too troublesome to implement?
Otherwise, it's really handy to have one interface that unifies deal alerts with all sorts of game metadata, with such extensive filtering capabilities. Great job on GG.deals! 🙂