Computer Help and Support

What happens is that malicious websites will hijack your browser to pop up warnings that take you to a non-MacAfee site that aims to hijack your money. They may ask you to download their "Antivirus" product, which ITSELF infects your computer.

These articles discuss how to deal with this, in degrees of sophistication,

https://www.msn.com/en-us/news/technology/what-is-the-mcafee-virus-pop-up-scam-how-to-get-rid-of-it/ar-AA14b42z

More detailed.
https://malwaretips.com/blogs/remove-fake-mcafee-pop-up-virus/.

I haven't vetted sites to see if their aim is to sell you their own antivirus product, but the base malwarebytes app is free (just not the advanced features) Some sites will give you the basic information, and then say "Well, it's SO MUCH easier when you buy our product"

If your system seems clean, then
The goal is to clean out any garbage that got into your browser's memory.

Asking others to comment if they have dealt with this.