I would pay at least double my current subscription fee for the ability to disable the undo request and the chat box.
You can change the ratio that the game log and game chat have on the right hand side by dragging the dividing line up or down (not sure if/how that works on mobile). That includes hiding the whole chat.
If the undo happens when your opponent has to do something (like they played a card but want to undo it), you can simply ignore it. If you have to do something (e.g. they forgot to buy something and ended their turn and want to undo to that point while you decide what cards to play in your turn) you have to respond at some time :-(