Chat isn't saved and in order to upload a screenshot, you would have to contact support after getting past the AI bots. It's not easy.
People who stall in losing positions can get their accounts closed. I just saw one closed last week.
I think just reporting is the way to go.
In the wake of an apparent loss, this person makes me wait indefinitely. I would have given them the benefit of the doubt if there were no messages, but this clearly crosses the line, IMO. Is there a way to email chess.com with these screenshots beyond just pressing the report button, or do you think they have access to chat?
Edit: I am not able to upload the screenshot of the chat. But long story short, this person clearly said he was going to make me wait 20 mins and hurled abuses.