As an extension of the Ultrawide community, this Steam group will identify games that release or patch in 21:9 resolution support.

/r/ultrawidemasterrace Group reviews

"Games that work with ultrawide (21:9) monitors for the ultimate immersive experience! Games that offer 21:9 support during "gameplay", but not cutscenes and/or menus will be approved. 32:9 reviews coming soon!"

Here are a few recent reviews by /r/ultrawidemasterrace Group