how can I know if my mac has a virus? is there any specific notification that I have to be aware about or is there anything that will help me detect it?

That notification is a scam - you will probably see a lot of these. No-one can remotely detect that you have a virus (even if that were possible - there are at the moment no viruses in the wild affecting Macs).

Without exception, all messages and pop-ups saying you have a virus, or that your Apple ID is locked and you have to 'verify' it, are scams. Never ever follow links or phone numbers given in these. Some messages may appear to come from Apple - real messages from them will address you by name whereas the scams mostly address you as 'Dear customer' or similar. if you feel the need to check your Apple ID you should go directly to the Apple ID site: don't follow links in any email.

And you don't need an anti-virus program, or a 'cleaning' program - many of them cause more problems than they solve. Some are aggressive and very difficult to remove. Macs have built-in protection. Your main danger is not from viruses but from malware - which is what you are likely to get if you start downloading the sort of programs I mentioned above.

As you've been told that message is a scam. No anti-virus or so-called "cleaning" apps are necessary or recommended for Mac. Your Mac's built-in security should be enough. (I would definitely avoid AVAST.)

That message is a scam. Do not use any third party apps that claims to protect, clean, boost performance etc. AVAST would be an example of a third party app to avoid using.

Try AVAST which is free anti-virus software for Mac OS.

https://www.avast.com/en-us/free-mac-security

I think you don't need such software, though.