How about an actor (pawn even) that is a sealed box room with a camera, its own lights (or no lights), a menu widget component, sounds and whatever else is needed. Place that actor where the player cannot reach it. Switch to that room’s camera when the menu opens or posses the room if it’s a pawn. Or teleport the immobilised player there.
That room is your menu. Rooms like that are often used for inspection system where you want to render target to UI.
Would that work for you?
Perhaps Streaming Levels are another option. You can have it loaded and show / hide it without affecting the rest of the world.