how do I download anti-virus software to my Mac OS Ventura13.4

I'll add my 2¢ worth also:

First, there is no reason to ever install or run any 3rd party "cleaning", "optimizing", "speed-up", anti-virus, VPN or security apps on your Mac.  This documents describe what you need to know and do in order to protect your Mac: Effective defenses against malware and other threats - Apple Community and Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support.  

There are no known viruses, i.e. self propagating, for Macs.  There are, however, adware and malware which require the user to install although unwittingly most of the time thru sneaky links, etc.   

Anti Virus developers try to group all types as viruses into their ad campaigns of fear.  They do a poor job of the detecting and isolating the adware and malware.  Since there are no viruses these apps use up a lot of system resources searching for what is non-existent and adversely affect system and app performance.

There is one app, Malwarebytes, which was developed by a long time contributor to these forums and a highly respected member of the computer security community, that is designed solely to seek out adware and known malware and remove it.  The free version is more than adequate for most users.  

Also, unless you're using a true VPN tunnel, such as between you and your employer's, school's or bank's servers, they aprovide false secutiry from a privacy standpoint.  Read these two articles: Public VPN's are anything but private and Former Malware Distributor Kape Technologies Now Owns ExpressVPN, CyberGhost, Private Internet Access, Zenmate, and a Collection of VPN “Review” Websites. 

The Operating System resides in a Sealed and Read Only Volume that can not be opened by the User nor by Third Party Applications.

The only Entity that can open and modify or alter this Volume is Apple.

That would occur when a update or UpGrade is performed.

The Only thing this Antivirus software is protecting is the Bank Account of the Developers and for zero return to the User aside from the problems this software creates.

AntiVirus Developers purposefully Market their product to create a “ Fear Factor “. In so doing, creating a False Need for their Product.

The The Built in Security  is all that is required to protect the computer.

Ventura 13.4 has all the anti-virus protection you’ll need already built in. The biggest problem with malware these days is what lies between the user’s ears. Using common sense to avoid clicking on sketchy web links, avoid downloading and installing software that promises the moon, and juts being careful about what you click on.

Follow on

If the User recently moved from a Microsoft Windows environment then your question could a Fair Question.

Reason, MS Windows does get Viruses, as Windows is a Large Target for Bad Actor Software Developers.

As for Apple macOS - Our Collective effort to encourage Not Installing any Antivirus Software remains - Not needed at all.

See: Effective defenses against malware and ot… - Apple Community

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

Do not install such useless software on a Mac. They very literally do nothing but take up system resources for nothing in return.

How do I download anti-virus software to my MacBook Air?

Why do you want your Mac to run poorly and be less secure?