That is impossible.
Mono = one single channel, so it can’t work on multiple channels.
The only way I can see this working (if you say that PT does that), is that PT infact inserts x-number of extra plugins as “Ghost plugins”. So you think you insterted one for all channels, but in fact there are multiple who are controlled by the GUI of the one that is visible. And that is the exact discription of a VST3 plugin.
But really, I do not see the point, not at all.
I actually find the VST3 plugins (which are doing the exact thing you are asking for) not very usefull.
I rarely find myself into a situation where I want all my channels being processed in the same way.
As an example, let’s take the most common channel format, 5.1.
I’m not going into differences between front, back and center, but the LFE channel alone should explain this very well. There is no thinkable situation, configuration or user case where we would want to process the LFE the same way any of the other channels is processed. I am very happy that I can insert a mono plugin into my LFE channel for applying Low Pass filtering, limiting, generating sub harmonics and everything else that comes with the use of an LFE channel.
HTH
Fredo