How to stop "Scam Norton, McAfee, and other warnings" on my iMac?

These "adds" appear every minute, including warnings, detections, and 'time to renew' and others, often several adds in succession.. They appear in the upper right corner of my iMac, about 3 inches long and 1/2 inch wide. An answer on discussions from 2023 said to remove unknown 'notifications'. I did. all of them, there were about 5, from old websites. The Norton 'adds' began a few months ago. I assume they are scammers, not the real Norton.

After I restarted the iMac, they began without Safari being on yet. What else can I try?

[Re-Titled By Moderator]