Hi CMJones,
If you’re using the BSP brushes these do not have the option of simulating physics.
If it’s a static mesh, you will need to make sure that the static mesh has collision setup for it in order for it to use the simulate physics option.
For more information about Collision you read about it here in the documentation: Collision in Unreal Engine | Unreal Engine 5.1 Documentation
Thank you!
Tim