Why I can't press "3 similar draw" thing?

When I played this match (I know I was terrible) but my opponent and me made 3 similar moves in the endgame, but I can't press "draw" button.

At the 86th-91th moves. It's bug or I missed something?

Because there is no rule about "similar moves" draws.

You should have pressed the offer draw button *before* you moved 90 .. Kh3

Your claim was too late - the position after (both white's and black's) move 90 did indeed occure for the third time (so claiming a draw at that time would have been successfull), but not the position after black's move 91 when you claimed a draw.