Both of the below plugins have the problem. The knob volume does NOT stay linked/synced if the volume is changed on the system. The knob volume will only stay linked/syned if the volume is being changed on the knob itself.
"Windows Volume Controller" and "System Volume"
The Elgato Stream Deck Plus doesn't have this issue and the volume will change in real time on the knob when the volume is changed on the system.