I have an A71 and this. It's close to the limit as to what the controller can support, but it does fit in it without issue. They are compatible.

Yes, according to our information, this should work with this product.

Stadia works with the controller. I'm not sure about the phone, but as long as the buttons are on the side of the phone and the USB-C port is down in the middle, it should work.

I can't tell you, but I have since returned the Kishi because the compatibility is very limited.

If you buy the kishi with the iphone plug, it will work for sure. I have the one for Android. Unfortunately, it is not compatible with CoD mobile. But otherwise, the workmanship, handling and extremely short delay are top-notch, I must say.

My slightly larger Note 20 Ultra fits in nicely, so the S21 Ultra should fit in, as long as the USB-C port is also down the middle it should be compatible too.

USB-C

Unfortunately not. This product is only compatible with Android.