how to know if your MacBook have virus?

With all these junk files, and recognition of your Mac being a frequent visitor of the site, seems you need to clear your Temporary Internet Files — Too many exist.

Use this Link: Clearing History and Cache - Apple Communities

Your MBA does not have a virus.

Popups cause no problem as long as you don't interact with them.

Cookies don't cause problems either.

You don't need any crapware such as MacCleaner install on your Mac. In fact is best to any third party apps which claim they will clean things up for you, offer you additional security or speed up your Mac. They are all lying when they make such claims. The Mac takes care of itself without any help from such things as those.

You can tell that your Mac absolutely does not have a virus because there are non known viruses that affect macOS.

You might have installed some other forms of Malware, but all known malware is blocked by the OS.

Adware is essentially a Trojan horse, but has yet to be declared so in the grand scheme of things.

macOS does not need anything that purports to clean, optimize, protect, or otherwise maintain your Mac.

Visiting a website cannot do anything to your Mac.

Visiting a website does not allow that website to scan your Mac for "viruses" or any other type of malware.