Infected file (or not)?

You are right on track by being suspicious of the infection report and removing VirusBarrier is the correct answer. There is no need to install any Anti-Virus on your Mac and doing see will only cause problems like you are experiencing along with heavy usage of your Mac resources slowing your machine down.

XProtect is Apples tool to combat viruses (malware or trojans) and is updated frequently. That is all you need.

No Problem. Another thing to be aware of is allowing Notifications from a website while using Safari. Some sites will provide a fake notification saying your device is infected if you have allowed the Notification. You can check what sites that have allowed Notifications by going to Safari > Settings > Websites > Notifications. In my opinion, it is best to have very few, if any, sites allowed to provide Notifications.

While you are at it, you can also check for Pop-Up window by going to Safari > Settings > Websites > Pop-Up Windows.

No. XProtect is the anti-malware/antivirus component of macOS. Get rid of any 3rd party antivirus software you have. It won't do anything but cause problems.