how to scan my MacBook Air for viruses

Clicking on links in unsolicited emails from strangers is never a good idea, but it takes a lot more than that to install malware. That sort of "drive-by" infection cannot occur on a Mac.

Suppose you received something like the following:

That's a real email I got the other day.

Let's suppose you fell for that pathetic attempt at authenticity, and you clicked the "Sign in" link it provided. That action would open a web page completely unrelated to the financial institution that would proceed to ask you to voluntarily submit personal information.

Those sites are usually fairly pathetic attempts at fooling you into believing the website is real.

Or, a similar scam would load a webpage that attempts to download something onto your Mac. First of all, Safari would then intercede and ask you if you really want to do that. Of course not, because you didn't expect to download anything, so you politely decline, or just close the webpage.

Just suppose you didn't do that though, and allowed the site to deposit a file on your Mac. It would go into your Downloads folder, where you would need to explicitly open the file. macOS would then intercede (are you getting the idea?) and ask you if you really want to open this mysterious file. Suppose you're gullible enough to do that. That's still not a problem. If however that file wanted to install something that could actively run and perform potential malice, macOS intercedes once again and requests an Administrator password to install whatever it was.

Let's suppose you did even that. At this point your qualifications to use any mechanical device more complicated than a microwave oven should be seriously called into doubt, but no matter. macOS itself cannot be maliciously altered due to a variety of protections incorporated in it.

Hopefully this puts your mind somewhat at ease, but lets return to your original question. Downloading and installing something—anything—regardless of the source, popularity, reviews from tech journals, "tech blogs", the "news", or alleged "trustedness" to "scan" your Mac for "viruses" is a far greater threat. That's how people get into real trouble. Don't do that.

There are no macOS viruses. If you are experiencing trouble with your Mac, describe it. Avoid The XY Problem.