There are loads of websites which
claim to be able to direct you to the best anti-virus program (or full security suite) for a Mac. The problem with many of them though is that they're actually a disguised form of advertising for specific products.
However TechRadar is well-respected and trustworthy. (Indeed, it's one of my favourite websites). See here:
https://www.techradar.com/uk/news/the-best-mac-antivirus-software
I note that Avast Free Mac Security tops their list of freebies if you only want an anti-virus program (rather than a full security suite). As Avast is also (it seems) the most popular freebie among AB's Windows users, it might be worth considering. (I use Avast myself and I'm perfectly happy with it). Otherwise Bitdefender Antivirus for Mac might be your best option.
If you want a second opinion (but still from a totally trustworthy website), see here:
https://www.macworld.co.uk/feature/mac-software/mac-antivirus-3672182/
They put Intego Mac Internet Security X9 marginally ahead of Bitdefender but, by reading the information on both websites, there should be enough information available to help you make your final choice.