The "U2 VDD - U3 VDD" designation refers to a net, a connection point that is used to electrically connect several pins or pads on a Printed Circuit Board (PCB) or in a schematic diagram within your project. Specifically, this net connects the VDD (Voltage Drain Drain) pin of component U2 to the VDD pin of component U3. Let me detail the components involved based on your project description:

Thus, the "U2 VDD - U3 VDD" net is ensuring that both of these components are connected to the same supply voltage. Connecting the VDD pins of multiple components together in this manner is a common way to ensure they receive the same operating voltage, which simplifies power distribution across the PCB or circuit diagram.

In terms of PCB design, these connections are typically made using traces on the PCB. However, the "Exclude from BOM" and "Exclude from PCB" properties indicate that this particular net might be a virtual or logical connection in your schematic to denote a shared connection point but not necessarily something that translates directly to a physical trace or component in the Bill of Materials (BOM) or on the PCB. Instead, it serves to logically organize and explain your power distribution network within the schematic.