McAfee Security thru ATT, Windows 7 - must update to Windows 10? Do I really have to?

Since Microsoft stopped supporting Windows 7 on January 14, 2020, some software publishers have updated their own products to remove support for Windows 7. 

I don't know what specific McAfee product you may have through AT&T.  McAfee says that its " business and enterprise products" will be supported on Windows 7 through December 31, 2021.  https://kc.mcafee.com/corporate/index?page=content&id=KB91432 

McAfee's position with respect to its consumer products is unclear. 

On one hand, it says, "CAUTION: Microsoft no longer supports Windows XP, Windows Vista, or Windows 7, which could put your PC at risk from new threats. McAfee strongly recommends that you upgrade your PC's operating system to a newer version as soon as possible. ... McAfee provides only "best effort" support for McAfee products installed on Windows 7." LINK.

On the other hand, the "minimum system requirements" for McAfee "Total Protection" includes "Microsoft Windows 10, 8.1, 8, and 7 SP1 (32- and 64-bit)."  LINK

If I were you, I would uninstall all McAfee products using the McAfee Consumer Products Removal Tool.  See LINK.
And then install a good, non-intrusive antivirus-only product. 

There are lots of opinions on the "best" antivirus product.  Do some reading here, where post #1 describes some general best practices and post #2 gives some antivirus recommendations:  https://www.bleepingcomputer.com/forums/t/407147/answers-to-common-security-questions-best-practices/  Those posts were last updated in October 2019, so they're only a bit out of date.  IMO, they are still good advice.