How can I remove the player’s control of the character and pause gameplay? Also, is there any way to add new controls such as for menu operation only when the blueprint widget is on the viewport?
If you pause the game with Set Game Paused, the gameplay will be stopped, but UI(UMG) will still work by default. So… You can add your widget to the viewport and after this pause the game.
Also, you can disable the input of your character by using Disable Input node, and also add your widgets to the screen. Adding controls can be done with Enable input node.