https://www.chess.com/analysis/game/live/120596425161?tab=analysis&move=40
[Edit - I forgot to mention it's a speed chess game.]
After 21.Be3+ black resigned. As you can see from the eval bar - the position is favorable to white so black blundered by resigning early.
He must have made the mistake I did in my head. It's not surprising I made the mistake. But it is kind of funny that a GM would "see" what I saw. He entirely missed the simple 21...Kc7. He thought he was forced to play Rc5 and then he's down a rook after white takes it.
Kc7 isn't much fun - ideally you want your king on the 8th rank behind your pawns - but it's not horrible for a GM. They are great at defense after all.
---
The right sidebar had something I've never seen before. It has no number for black. I've seen 0.1 seconds but never nothing.
I assume white's move and black's resignation were within 0.1 of a second of each other so the site interpreted that to mean they happened at exactly the same time.
The eval bar is key. +1 for your opponent isn't awful. Like I said in the body - black is a gm so it's 100% playable at that level. For me - I also wouldn't resign at Kc7 but I'd certainly be having no fun. I like my king ensconced in a corner behind pawns until the end game. Defense is a real weak point for me.