You'll need to do it before going into focus mode, I think, and once disable it can't be enabled again for that game.
https://support.chess.com/customer/en/portal/articles/1444900-how-can-i-play-without-receiving-chat-messages-from-my-opponent-
You can also disable chat by default in the live chess settings.
I use the Focus Mode in v3, where there is no chat window. That's great, but when my opponent types something, a red mark appears and is distracting. I have to go in and out of FM to read their posts.
Yeah, I know I could try to ignore it, but it's there -- like a blood stain on the wall. It whips up the whole curiosity vibe, and I'd rather not deal with it.
I've noticed that some of my opponents disable chat. How is that done? I tried the "/help" thing, but it was no help. Thanks.