It is true that the Stadia topic is not a forté in many gamers' minds, particularly those who don't believe in the Cloud Gaming concept that Google (re)started (and many followed later). But it seems that there are some that keep good faith.

Developers like Hopoo Games and publishers like Gearbox Publishing are one of them and it is a surprising novelty that Survivors of the Void, Risk Of Rain 2’s expansion, is ALREADY AVAILABLE in Stadia, ahead of consolas and PC.

Embrace The Void as it overtakes Petrichor V in Risk of Rain 2’s first-ever expansion! New survivors, monsters, stages, and a new class of items have arrived to help you kick the crabs back to their dimension.

The expansion for Risk Of Rain 2 was bound for Q4 2022 after Gearbox announced previously of the delay for other platforms and initially, Stadia was included for the delay, so in my best guess, I think that Hopoo Games found an opportunity to test waters with Stadia before consoles and PC’s launch.