Investing customers money, create money.
Most money in the world is digital already, there are many banks that don't have physical presence and traditional banks are shutting down branches more than the open because branches are just the foot soldiers. There are also countries where cash is almost not used. Banks are not about cash, they are about credit.
I don't know what a "physical bank" means though, AFAIk there's no such thing and the buildings that banks own or operate would serve functions like hosting employees/clients/systems but they might choose not to have some of those.