How to globally disable notifications?

I consider Ux notifications (pop-ups, etc.) to far more often be a dark design, than actually beneficial or even simply neutral.

The version of Gnome Desktop packaged with Ubuntu 20.04 is aggressive about letting every application invoke notifications, and is—ostensibly—organized along an opt out model where I have to manually configure settings so that, say, the calculator is not privileged to annoy me with notification features:

How can I:

• Globally disable all notifications with one command, or one Ux interaction.

• Make such disabling permanent (i.e., if I manually click through the dozens of application’s multi-toggle notification preferences in Settings, a short time later—On reboot? On logging out and back in?—they are all back to full notification status).

• Permit/opt in Evolution/Calendar event notices, and only Evolution/Calendar event notices to remain active?