I'm not sure if this will work for anyone else, but I just got an update for my Chrome browser so I installed it and was like what the heck I'll try Stadia on Chrome. I'm now getting an excellent connection instead of I always used to get good connection and wouldn't you know it, I also am now officially running 4K HDR in Chrome! My display is a 43" 4K HDR Samsung Smart TV in case anyone's interested.
Edit: I jumped the gun when making this post. There is no "official" HDR for Stadia on Chrome yet.