The chat window has been bugged since the latest Deadlands patch on Google Stadia (at least when playing on mobile or with controllers).
The chat is stuck in the bottom left corner of the screen and can't be controlled with chat UI settings in the settings menu. Just as an example, if I wanted to increase the text size of the chat, choosing the "Large" text option in settings does nothing. Choosing to hide the UI also does nothing. Playing on mobile, the text is very, very tiny as it is now. Prior to the patch the chat was in a good position on the right side of the screen, the text was readable, and we could control the text size and other settings in the settings menu.
Obviously something got messed up and it just seems that it's permanently stuck in "keyboard mode".
I had sent in a bug report ticket when the patch launched on Stadia a couple weeks ago and haven't seen any updates or acknowledgement of the issue. It's actually made me stop playing since then because of the annoyance of having chat take up and hide a good portion of my screen (especially on a small display).
Checking Reddit, I can see other Stadia players have had this same issue, so it isn't isolated to me alone.
This is me playing on my 5.7" phone; the chat text size used to be comparable to the size of the text of the quest tracker items and located underneath it: