3N is balanced choice of game, 4♣ and 4♦ are cuebids, and 4N RKC
So you have to lead against 6♠.
A simulation shows that ♦ is best so you lead ♦8 and see the following:
First trick goes 8->9->T->K
Declarer plays ♣A followed by a ♣ to the Queen. Partner follows with the ♣2 and ♣T
Declarer now plays ♠J-2-9 and you take the King.
Now a new simulation shows a chance for an uppercut if partner has ♠T, so you play back a ♣, but partner has no more trumps and declarers 2 losing ♥ go away on the ♣.
The interesting part of this board was declarers play of ♠9, as we know he must have one lower, so why play ♠9?
For a human it is obvious that there is no uppercut, but that is not clear for the bot.
I ran a simulation if declarer had played a lower ♠ and now the best continuation was a ♦.
So the clever declarer dropping the ♠9 gained 13 Imps instead of losing 13 as the other table played 4♠