By default, supply voltage for logic parts, digital inputs and outputs, digital ICs, and microcontrollers is hidden. You can edit it through the scene properties.
To create a realistic 3D printed circuit board, you must supply voltage to the circuit explicitly.
Add a power connector to the 2D view of a PCB 3D space and connect it to a power supply. It will now supply voltage to the parts that require a voltage supply in the PCB 3D space.
In the 2D view, the power connector does not connect directly to the circuit but provides virtual connections to all the parts that require a voltage supply.
In the 3D view, the power connector is hidden. Once the PCB is routed, all the virtual connections to the voltage supply are represented by real tracks on the PCB.