The ugly brilliant move! Volume 1 What is black's next move?

This game is between Liao Yuanhe 9P and Lian Xiao 9P, black wanted to block the top right corner, what is the move?

In the real game, black played 1, 3 to block the corner with force.

It became a ko afterwards.

White 1 started the ko and lead to an exchange, AI think black is a bit in deficit.

Black 1, a very strange move is what AI recommend.

If white 2 jump, black 3 is brilliant.

Black could avoid the ko!

If white 2 nobi, black 3 could attach to divide the white.

White 2 is trying to pressure black's corner.

Black 3 is not reasonable, white 4 is too great.

Black 3 should defend calmly and AI think these exchanges are a small gain for black, it is much better than the real game.