How can I delete MacAfee forever?

You don't have McAfee, and never did. A site you visited added itself (or you clicked a button) to allow notifications. Everything you're seeing is nothing but a scam.

Open Safari's preferences (Settings). Click on the Websites tab and then scroll down to Notifications. Clear any entries in the right hand window. You might find something similar in the Pop-up Windows heading below that. Block any you don't recognize.

Then if you want, uncheck the box to the right, as shown below here.

I personally can't think of any reason why I would ever want any website to push notices to me.

If it is listed in Notification menu then just turn off. Also if you have MacAfee app then move to trash or use the app "AppCleaner" to find most if not all MacAfee related files to delete. You do not need this app ever.

Block pop-up ads and windows in Safari

Block pop-up ads and windows in Safari - Apple Support

Stop unwanted Notifications - John Galt

Stop unwanted Notifications - Apple Community