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What I'd really love to see is a platform icon in one of the corners of the game tile so you instantly know to which platform it belongs. So you don't have to hover over tiles and wait for popup to tell you, you'd just know instantly by looking at it. Might not be an issue for some, but I have a lot of games that share platforms because I got them from different sources or bought twice or more times, but prefer to play on a specific platform, that's quite important. And you wouldn't have to fiddle with filters and bookmarks. It would just be right there in our view.
We already have platform based filters, but I must agree this may be useful to avoid confusion about some game's origins.

A truly best solution to this would be a universal "GoG Connect" like program including all platforms and without restrictions. But I'm afraid this is just utopia.
We do have platform-specific filters, but I can think of two usecases off the top of my head where icons on the game tiles would be handy:

Use Case 1: Installed games

The installed games filter is supposed to show you all games installed on your machine. Say you have two copies of KOTOR 2 installed, the GOG version and the Steam version that's bundled with TSLRCM. Which is which?

Why would you have two of the same game installed? Perhaps you modded one game, and kept the other pristine. Or you're running different versions (Say, latest beta Stellaris through steam and the stable from GOG).

Or, the case may be that you have duplicate games you want to uninstall.

Use Case 2: picking the right game to install

Say you have a game that's been on multiple giveaways/bundled. Say perhaps you own Mutant Year Zero on GOG, Steam, and EGS (I don't on GOG, but I do on the other two). Say you are browsing the "All games" page to see which games you have, and which you want to play. Say you are not using the platform filters for a reason, because then you'd see the same game perhaps 3 times while viewing different filters, and install three copies of the same game (see Use Case 1 above).

There are reasons to have platform icons on the tile screen.
I think the way to do this would be to have an extra option to only show the icons on games which are owned on multiple platforms.