Only option is to wait until more resolutions become available. Currently this is one of the limitations that were made known just prior to release of Stadia.
You could try temporarily setting your OS resolution to 1080p as a workaround.
Not that this is ideal, but if you run windowed it looks more normal. I found some Chrome extensions that do it. I'm really looking forward to it being fixed too.
@unrav3l : Most monitors have a ‘native’ resolution. Any other resolution that is not the native one is about as random as it gets if it is usable or not. It isn't the fault of Stadia that it doesn't look usable in 1080 on your hardware as your native resolution isn’t yet supported. I on the other hand have a native 1080 resolution monitor and Stadia looks just fine for what I am accustomed to. Unfortunately I don’t see any other options available where the output will look great for you if your monitor doesn't do a particularly good job when it comes to mimicking 1080 resolution on 2440 hardware.
@Mad_Dog_Bravo It should have support for upscaling 1080p to abitrary resolutions, though.
@Jop : Yes, although what the technical implications (if any) would be I have no way of knowing. But that ultimately is a feature, which may or may not have priority, once again I can't tell, as there is no publicly available feature road-map.
What was discussed recently on Reddit was the following:
https://www.reddit.com/r/Stadia/comments/dvv3tv/hi_reddit_andrey_from_the_stadia_team_here_and_im/
I've included some of the points discussed below:
So, personally speaking, I'm happy that Stadia was designed to be released on the biggest screen first. 1440, 2440 and other screen resolutions will have to come later in due course if that is the goal, but I prefer without question to play on the largest screen we have in our home, which for me is our living room television.
@unrav3l : It might be that running Stadia in a 1080 window might be the better (temporary) solution for you...?
A couple of links that I saw earlier today included:
http://www.brianapps.net/sizer4/ - used to accurately resize and re position windows
https://chrome.google.com/webstore/detail/windowed-floating-youtube/gibipneadnbflmkebnmcbgjdkngkbklb - used to keep Chrome full screen as a window
It might not be to everyone's liking, but by the same token might make the issue a little more easy to manage until such time that Stadia supports a wider range of resolutions.
Hope this helps.
@ChrisFromGoogle did say they do look at the forum but they are enjoying time off and having delicious thanksgiving this week/weekend but I assume they know people want love for their ultra wide monitors so we can get some high quality pc goodness on our screens @GraceFromGoogle