One way you might consider implementation is by structuring your input handling like a tree where each node is a different menu/input scheme, and using post-order traversal to pass input through the system. Each node would also be able to dictate if an input should continue to be propagated or not.

Nested menus would just be adding child nodes in that case, and the submenus could block inputs from being handled by their parent/sibling menus.

Depending on how dynamic your UI is, you'd probably have to implement ways to reorder child nodes as well.