I wonder why the support specialist recommended I install Malware Bytes.
Because getting adware is something you cannot prevent. And, malware can show up if the site you are visiting is allowing links or ads that contain hidden malware. Malwarebytes is one of the few apps that is indeed recommended by Apple.
Although there are no viruses that are currently targeting Macs, the other two can show up on your screen unexpectedly. That would be the time to run Malwarebytes. I have it installed but will only run it if I do get some adware. I do not install AV ware.
I will give you an example: Some years ago one software developer hijacked by browser (Safari!!) - the entire screen was taken over with flashing signs that I had 8,546 (or something like it) viruses, but they would get rid of them if I clicked here and paid them money. Otherwise the computer was not responsive - mouse did not work, keyboard did not work, I could not quit Safari, nothing worked. I had to shut off the power. At the time there was a feature Apple had just come up with that if you booted up the same window would open by default. So, I was unable to boot up or work on it. I had to boot up from an external source, wipe the entire drive, and then clone back the backup clone I had. It took two days to get it working.
So, to say that you are "fully protected" may be what you want to hear, but it is naive at best. The OS is now contained in a read only volume and that is very good regarding viruses, but adware does not need to access that to install itself in your browser. Yes, you generally do not need any AV ware and your OS is quite protected, but adware or malware can happen. And in that case you will need something to get rid of it.