this guy is cheating ig

20 best moves and 84% accuracy are normal parameters, even for a 400 rated player.
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He could well be capitalising on early blunders from your opponent.
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For example, if the game lasts 6 moves, your friend wins the game by checkmate and your friend makes 5 best moves (including the checkmating move), then his accuracy will be around 5/6 x 100% = 83.3%.

https://support.chess.com/article/209-how-do-i-report-someone
If your suspicious please report players
Thanks