Hi don't know if it has already been suggested but I was thinking it would be useful to have a cancel button in the game. Situations such as clicking on the extra deck to special summon and not wanting to/realising you cannot make the monster you wanted to. It could also be useful for clicking yes to chaining a card, e.g. accidently wasting a necro gardna or veiler - however this option would slow down the duel for the other player so is less important than the first.

Nomad Trooper
There is a cancle button.

Read the FAQ :
Q18. How can I cancel a move?
Answer: Most moves can be canceled by clicking on the right-mouse button.

Also of interest:
How can I force the activation?
Answer: Press and hold 'A' to force activation of cards

And holding S I believe will auto select no for any activation queries.
Thanks for the info 🙂