Digispark 5V Output Problem
The USB specification defines many states that a USB device can be in, depending on how the host interacts with it. But when there is no activity on the bus (on the D+/D− data lines), the device must go into the "suspended" state to save power:



The only state in which a device is allowed to draw much power is "configured".
So unless you manage to communicate with the keyboard (which requires implementing the electrical USB protocol, and a huge USB software stack), the keyboard will not power up.