Shouldn't black win this one?

https://www.littlegolem.net/jsp/game/game.jsp?gid=2427936

Yep, since both players passed, black should win. The autoscore knows more than the players though and takes this into account: https://senseis.xmp.net/?BulkySevenInTheCorner

That's the problem with using an AI for autoscoring. It can come to conclusions that neither of the players understand.

Yeah, black should win here as both players declined to play on from the position.

On top of that, how is victory being awarded by a whole point margin when komi includes a half point?

White has 12 point
black has 22 point
white komi 6.5
black win by 3.5 point

There is any error for autoscore :)

Maybe two systems of scoring, if they agree it's a result, else if players agree it's a result, else play continues with each player not passing first time

What I find strange is that black wins by Chinese rules even with a seki in the upper left corner. Plus I do not understand how it can be an integer score when the komi is 6.5.

Katago usually gives value estimates like B + 3.38 points, even if the game is fully decided. Probably some incorrect rounding to integer involved, instead of rounding to integer + 0.5