Has my MacBook been hacked?

The messages might not really be from McAfee. It's common for criminals sending "phishing" messages to claim that your device is infected with viruses, has been "hacked", etc. They want to panic you, the better to get you to help them scam you.

FTC – How To Spot, Avoid, and Report Tech Support Scams

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

If these messages are popping up in the upper-right-hand corner of your screen, they may be Web notifications. See the following User Tip, which shows you what these messages look like and how to block them.

Stop unwanted Notifications - Apple Community

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P.S.: Here's an example of an actual e-mail from criminals pretending to be "Norton". I wasn't a Norton customer, or a "Norton payment solutions" (LOL!) customer, and there was no order. The supposedly "authorized" payment was completely fictitious. Had I called the number in the e-mail to "request a refund", that would have been when the criminals would have gotten the financial information with which to carry out their scam.

Perhaps a persistent notification from browser history reports

what its maker intended, to show a message for you to deploy

their useless product; it might be the real meal; not satisfying.

..There may be some other thing(s) going on, but no virus..

[In an iPhone, you could look into Safari settings and Clear History.]

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

//support.apple.com/en-us/102568

(Generic item, location may vary between iOS or macOS versions)

Not certain if third-party browsers in use, also might clear history.

Also you may try Safe boot mode to see if the symptoms change

through its use; some times there is a change. Or that may remove

the symptoms entirely by using Safe mode on startup; & restart.