Give an ability to scroll up the in-game chat.
Someone might be flaming a player in-game when the person is AFK, or the chat is spammed so he couldn't screenshot what the other dude said but he still can scroll up the chat by pressing a certain button to screenshot it and report the user.
or someone is advertising and the chat is spammed but unfortunately people couldn't screenshot it so they still could ss it by scrolling up the chat.