I was able to start a stream session and it did come up, although it kept reporting connectivity quality issues and it seemed like it was streaming at really low-bandwidth.

However, I normally stream via Sunshine/Moonlight and haven’t tried the native Steam version in a while since it normally doesn’t work well for me, so I think that’s something on my end rather than it being a bug (and the fact that it displayed the game to me indicates its no longer this bug, since it initialized and was at regular brightness).