Same problem here but fixed it! I ended up going into options and setting everything back to defaults and then it showed up as holding down the ... in the keymap.
I finally found a solution. From the Stadia iPhone app, launch a game and select the Chromecast ultra from the dropdown. Doing that will bring up the "all this app to connect to devices on the netw...
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I finally found a solution. From the Stadia iPhone app, launch a game and select the Chromecast ultra from the dropdown. Doing that will bring up the "all this app to connect to devices on the network" prompt which you need to allow/agree to. Once you've successfully launched a game your Stadia account will be linked to the Chromecast Ultra. Edit: The next time I tried to connect, it once again told me to add my Stadia account to my Chromecast via the Stadia app on iPhone, but now it was in the list; I believe since I had already launched a game via step above.