For an stereo audio track, is there any method or third party plugin that can be used to mute of one of the left right track or adjust the volume of left/right channel?
You could just make the stereo track dual mono. Project/Convert Tracks, select the mono option
This would basically give you Dual Mono like Protools and allow you to adjust volume on each as well as panning.
If needed you could select those and right click, add group channel to selected tracks if you needed to move both volumes at the same time but not lose the overall balance you had individually.
Peter;
In Cubase you can have a stereo track and the pan is a pan. You also can have a 2 channel mono track and pan becomes a balance control its still pan though. A mono track with a single channel has a pan control.
If you want to adjust the left or right channel of a stereo track use pan.
There are plugins that can work with mid side processing on a stereo track. There are also width control plugins.
Also, svennilenni correctly answered your original post question with the suggestion of using Steinberg’s supplied Mix6To2. The only issue with this plug-in is that there are no associated mute buttons in the interface. But easily solved by clicking at the top or bottom of the fader tracks to simulate an instantaneous mute/unmute.