Here are the highest I'm aware of:
-Highest OTB is chess world champion GM Magnus Carlsen who has been over 2800 elo for over a decade now.
-Highest on chess.com is GM Hikaru Nakamura @Hikaru at over 3400+! Incredible! Also, Magnus Carlsen and a few others are around that level online too, but there are so few chess players even over 2700 online and super super few over 3000 rating.
-Highest computer I'm not so knowledgeable about, but Stockfish at real maximum difficulty (stronger than live analysis server Stockfish computer chess.com uses) is over 3500 I believe and other computer engines like Komodo or AlphaZero are even stronger, probably close to 4000 I'd imagine. Maybe 3800 or something like that.
I’ve always wanted to know the highest chess rating in the world including cheaters