I don't know how the chat is supposed to work, so I cannot know exactly what the problem is. I can only explain what I experience, which doesn't make sense.
When chat is turned on, I constantly get a popup saying to turn chat on and type something. I use the Chromecast Ultra to play on my living room tv with controller(like a console), so I can't possibly type. I think the system automatically assumes I'm playing on pc with mouse & keyboard. Because of this, I have to keep text chat turned off.
However, yesterday I was playing with clan members. One on Xbox, one on PC, and I on Stadia. I could voice chat with the guy on xbox, but not the one on pc. The guy on pc could not hear us chatting. Although, the guy on Xbox could see the text chat onscreen and I couldn't. It was a messed up way to communicate. Guy on PC couldn't hear us, and the guy on Xbox would have to tell me what the guy on pc was typing on the chat.