I want to control a showing and hiding elements from backend.

So, my main goal is to code a button, whose access will be with me/admin. And when I click on that, all the users currently on the page or accesses the page should see a strip/ an image/ form/ or any other element that is already made before hand (It should not appear before a click). And then I should be able to hide the same with another button or the same button. Note: The user needs to reload the page is not an option.

Why do I need this?
I am making a website that would allow my client to host his own personal webinars on the website. So when he introduces his courses in his introductory course, which the users are attending, at the same time people should be able to see the form or any other element. Since it is going to be live we cannot really depend on the any time like show up after 1 hour 30 mins or any time like 3:30 UST.

I hope you understand my issue, I went through many articles present on this forum, but couldn’t find solution for the problem.

Thank you,
Mayur Agarwal