I own a 2000 WV PASSAT B5, and the main problem I am having is that the driver-side door mechanism does not lock all 4 doors. It only locks the driver's side door and does not arm the alarm. But when I lock the doors from the front passenger door, every door in the car locks like normal and arms the alarm. I have a suspicion that it is a blown fuse or other electrical issues.
Having looked at the fuse wiring diagram for your vehicle there are no fuses specifically for driver versus passenger side door locks. They are all tied to one fuse, so likely it is not a fuse since the passenger side is working properly. Therefore, it is likely a bad switch or frayed/broken wire leading to the door switch. The wiring for the switch runs from the body to the door where the door hinge is located on the front of the door. The wires are typically in a black, ribbed wire loom. You should check this first because of the frequency of opening and closing the door which often causes frayed or broken wires. This is a common issue especially in older cars. You can cut open the wiring loom with a utility knife and visually inspect the wiring looking for frayed or broken wires. If the visual inspection reveals nothing unusual you can check if power and ground are making it to the switch using a multimeter. There are a number of videos on YouTube that can show you how to do this. If that checks out you have then isolated the issue to a faulty door switch.