I haven't really kept up with this thread since last posting as other work priorities took over, however I'm back to revisiting the Voice Control problem, both on Catalina and Big Sur.
@Jon_K I couldn't find any shell commands to turn on Voice Control when I last looked into this, and I did research extensively into it before I ruled it out.
I found that there was a file that could be altered (can't remember off the top of my head at the moment which one) that did result in the check box for Voice Control being checked, however it did not actually launch dictation or voice control in the initial instance until going in and manually toggling the check box (which then resulted in admin credentials box), It's as though the act of checking the box also launches a process, and I couldn't work out how to call that process by any other method.
On subsequent logins after Voice Control had been turned on at least once, it did launch the Voice Control service but in my environment this isn't workable to have to manually enable the service for every new user at these computers, from an Administrator.
@kareem33 Yeah it's frustrating that there are issues with this, particularly when third party vendors (Nuance / Dragon Naturally) dropped out of producing for macOS due to how difficult the operating system is getting to develop for due to Apples security hardening.
/start rant... I'm all for a secure operating system, but hardening the system while providing such a detrimental affect to security and product options is not a great outcome for users. As an admin of a company who is buying hundreds of macOS devices per year, the lack of MDM toolset functions to adequately manage usability settings like this is incredibly frustrating, and leading us to develop hacky work arounds which ultimately compromise the security and integrity of our overall environment. /end rant.
In answer to your question, Yes you would be able to toggle voice control off in the same way, I believe there is also a phrase you can enable to turn voice control off in the voice control settings if that is easier. It is unticked by default, so you'd need to go in to voice control commands to enable it. (Technically you could automate that too)
If you need to turn it off and on regularly you could say "Turn off Voice Control" and then follow it up with "Hey Siri, Turn on Voice Control" to avoid scripting. (assuming that voice control would be responsive to you)
Anyway, My organisation are looking at this again, I think on the few computers we'll be using Voice Control on we might bite the bullet and make the users Administrators rather than standard users, however this makes us a little uneasy at the thought.
I did also feed my comments on Voice Control for standard users back to Apple through the appleseed beta program for Big Sur... disappointingly, I never received a reply.
If I have any breakthroughs, I'll update this post.