Virgin Media's security offering is dependent on F-Secure and their product's requirement is for recent versions of MacOS.
Sophos Home Free has been mentioned a few times on the forum so maybe worth considering; their system requirements are: Mac OS X 10.12, 10.13, 10.14, or 10.15; minimum 4 GB of free disk space, minimum 4 GB of RAM. There are other alternatives and I would encourage you research those as well to find the best fit for your needs.
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