Anti virus protection

#1) How can I tell if I got a virus?

You don't.

Not only are there no viruses that affect macOS (as in, zero) it is not possible for malware to infect your Mac by merely clicking an email message. It's a good practice to never click links in an email message though, because they may redirect to scam websites that may in turn attempt to deceive you into doing something you should not do, such as revealing personal information to a scam website. Avoid fraud by using encrypted websites in Safari on Mac describes how to avoid scam websites.

Scam websites are extremely common and a different subject altogether, but an email itself message can do nothing just by opening it in the Mac's Mail app. Read Identify legitimate emails from the App Store or iTunes Store for additional information on that subject including phishing and other scams, but the direct answer to your question is NO. You don't have a a virus. Reacting to a scam email by installing some non-Apple "anti-virus" product is not only unjustified, it is the first step in a well-worn path to misery. Don't go there.

No, I don’t have anti-virus software.

Since you are using macOS Catalina yes you do. The Mac operating system is impervious to viruses. Not only does macOS itself incorporate a wide range of built-in protections against malicious alteration, it runs from a separate, "read-only" container. It cannot be altered outside of macOS updates and upgrades that only Apple hosts on their secure servers. Keeping macOS updated is a fundamental defense against emergent threats. Keep your Mac up to date describes how to accomplish that.

Placing one's reliance upon some company that claims more macOS knowledge than Apple itself is a foolish approach to computing security, which takes you to your next question:

#2) what anti-virus software is recommended to get?

None. All non-Apple "anti-virus" products are not only categorically useless, they will increase your threat profile when your goal ought to be to reduce it. Install nothing of the sort. Read Effective defenses against malware and other threats for more on that subject.

#3) I’ve already asked this question, but I can’t find a reply - how can I do that?

If you want to find your own previous Discussions including replies you posted to other Discussions try using the My Subscriptions link at the top of these pages.

macOS Catalina itself should be safe, since it's on a separate partition from the rest of the system. And you don't have access to it yourself.

Virus wise you should be safe. Basically no viruses for MacOS. However scam mail generally installs malware so you might want to run https://www.malwarebytes.com/mac/ The free version should work there.

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You're very welcome.

It's not surprising that the link just loaded a blank page, but literally nothing can come of that. Close the page, delete the email, and forget about it. You're fine.