Just gonna throw in a wish here, aim for the stars and all that. I would be pretty darn excited to see Euro truck sim 2 on Stadia, especially if devs add in official multiplayer support. I know it's not exactly something to expect, at all, but who knows?
Google Stadia cannot influence that, the developer must want to.
But what you can do you are welcome to give feedback via the Stadia menu that goes directly to the Stadia team, other players may also request this game and Google can go to the developer and say Hey the players want your game on our platform
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