Maybe I missed an update...but Stadia now works on my Oneplus 6. Not via the app though but using the android chrome browser and using the desktop view/site option. I know for certain that this didn't work before because I tried it but it seems to be working now?
Quick update, just connected my controller and it seems to be working fine...
Does not work on iPhone through chrome.
I tried it after reading your post and it works on my Samsung S10 aswell! Thats cool!
Did you by any change recently update your S10 to Android 10?
This could be reason why it suddenly Works.
Nope OxygenOs 9, which is the oneplus version of android 9.
Worked aswell on my lenovo tablet and samsungs7
But as stated above must use desktop view on chrome on the Stadia page and not go trough the app ( if you are not using desktop view on chrome the stadia page will just redirect you to download the app)
So now is the wait too be able to connect controller trough bluetooth on mobile and tablet instead having to use an usb-c
Have you tried a PS4 or Xbox controller via Bluetooth? It use to work but I've had a chrome update since and now stopped.