Malicious popups
I wonder how many people have had this problem? I had nasty popups appearing at 15-minute intervals telling me that my system or iCloud or gmail etc..were infected and I needed to click on the popup for an anti-virus scan. A clue as to what to do was supplied by someone in the Apple community and I followed through - if you get these then, Go to Safari settings > Websites > scroll down to Notifications and then you will be able to identify the invader listed in the Panel. Highlight this and click on Remove.
MacBook Air (M1, 2020)