Unfortunately, the default limitations on screen sharing are a basic part of Macs' security. The program needs to be run before the permissions can be enabled. So it would not be realistic for us to run each program and set up permissions for all the different sharing options for each conferencing app.
I would like to be able to send you clear instructions for each conferencing software program you may run, but the rules are different depending on whether it's browser-based and which browser you're using. Additionally, every time Mac releases a new version of the operating system, the controls change.
I suggest using Safari if you are doing a web-based conference. Since Safari is part of the Mac operating system, it is simpler to confirm the permissions with Safari as it usually doesn’t involve editing System Preferences.
If you
strongly prefer to use Firefox or Chrome, you'll need to give the browser
screen-sharing permissions in real time in the System Preferences menu. Usually
a message pops up guiding you through that process. You may need to edit the
System Preferences as an admin (again, it depends on the software and what
you're trying to do). If you do need to be an admin to make the changes in
System Preferences, please use Admin By Request to enable a temporary admin
session. Here are instructions for using Admin By Request to request a session
as an administrator.
FYI, this is only a Mac issue. On a Windows device, the workflow to share your screen from a meeting is much simpler.