Signs of a CheatEr

https://support.chess.com/article/648-what-do-i-need-to-know-about-fair-play-on-chess-com
Discussions of cheating, potential cheating, or cheat detection are not allowed in the general forums.
https://support.chess.com/article/648-what-do-i-need-to-know-about-fair-play-on-chess-com
Discussions of cheating, potential cheating, or cheat detection are not allowed in the general forums.
what are the signs of a cheater for you? what do they do and you say; okay.. this is cheating.
lets say <1000, 1400 & 1600+
I once saw a GM cheated on a twitch stream. He was down on material but was in a 'theorically drawish' position, still it required exact moves to defend.. he did some bad moves first and then went for toilet, closed screen, came back in 3-4 mlns then he explained how to defend, what are no-go moves in that position. And he played and drew it. He was babling about how well he knew that tablebase position which he was clueless a few mins ago.
Anyways, what are dead giveaways of a cheater? How can you spot him DURING the game, not in aftergame analysis?