The Razer Junglecat is an Android Bluetooth controller that attaches two thumbsticks to either side of a gamer's phone. However, this orientation is only compatible with a handful of devices. The Junglecat can be used as a standalone controller for other Android phones and PCs. The Junglecat is available for US $100.
https://www.notebookcheck.net/Razer-s-Junglecat-controller-turns-your-Android-phone-into-a-Switch.440553.0.html
Razer Phone 2 + Junglecat + Stadia should be awesome. I just don't like the price point :)