Not to be confused with chat text size, there's no available scaling option for chat box on iOS.
Edit: No way to move chat window, I tried with a 2 finger gesture to check if it was meant for something like that.
This may have to do with the resolution displayed ingame.
Related image: (part of the text is unedited to demonstrate size, text size was set to small before screenshotting)
Consequence: This may cause text to appear pretty much near the center of the screen, instead of being downscaled towards the bottom left corner of the screen with no way to scale it.
Current workaround: choosing a chat tab where no one is talking.
Specifications:
iPadOS Version: 17.2
Model Name: iPad Pro (11-inch) (4th generation)
Resolution: 2388 x 1668 px at 264 ppi