How can I get rid of the hundreds of pop up windows from McAfee??

You're being bludgeoned by notifications. Nothing at all to do with popups or extensions.

Safari > Preferences/Settings > Websites

Scroll down in the left column to Notifications. Remove any entries at the right.

In addition go to Safari > Settings > Websites > Popup Windows. Remove all, unless known site you allow a pop up.

Go to Safari > Settings > Extensions. Turn all off or remove.

If you have McAfee installed and want to know how to remove, please advise further.

Go to Safari > Settings > Websites > Notifications. Remove all.