Stereo or Mono for mixing VSTi ?

I found that using any kind of VSTi in Cubase, say addictive drum, kontakt or whatever are stereo in nature.

I saw people mixing drum (e.g. kick, snare, tom) using a mono audio track.

So is that necessary to mix drum in a mono way?

If yes, then what should I do with those stereo vst tracks?

Bouncing it into mono makes the tone distorted and splitting it into L/R(and giving up one) would also result in tone change.

So in short what’s the proper way to handle with these stereo vsti?

There is no proper way - you do what you think sounds right for the given context. You saw people mixing drum on mono audio track, cause usually that´s the format these sources are recorded at. That doesn´t necessarily mean the whole drumkit has to be mono - but it can, if this sound is desired.