When any opponent plays a card like Militia or Margrave I am able to choose the cards to discard but there is no button available to confirm the discard decision. Only an undo button is shown and also the options Undo or Resign, but possibility to continue the game
After two clicks on cards in your hand (for Militia, respectively three for Margrave) you should see a button [CONFIRM DISCARDING] - see below how it looks on my screen after a Militia attack, having selected two Estates.
If this doesn't appear for you, which device/OS/browser/screen resolution are you playing on?
After chosing the two cards to discard no button like "confirm discarding" appeared. I played on Windows 10 using Firefox. My resolution is 1920 x 1080. The screen was moved where the lower part of my cards are cut. Maybe the button "confirm discarding" was hidden is that part I can't see.
When I set the Option "Move kingdom and play area" to YES, I still see that "Confirm Discarding" button - see my screenshot.
This is also on Windows 10, Firefox, 1920x1080. Can you maybe post a screenshot?
It looked like the screenshot you showed in your last reply. I think the option from that you wrote will be very helpful for the future. :)
Unfortunately, I missed the opportunity to make a screenshot from my buggy situation.