Do not allow http or ftp traffic as this guide suggests, unless you are active as a server for your local network on those particular ports, and you are behind a NAT firewall that your router usually provides.

I love that Mint brings people to Linux, but its users write some silly guides sometimes.

Don’t concern yourself with hardening.

Just use your computer like you normally would, solving issues as you encounter them.

Don’t let people drag you down rabbit holes.

For another view on installing antivirus software on Linux, see this: https://easylinuxtipsproject.blogspot.com/p/security.html?m=1#ID1.1

That’s actually a fairly solid guide/list.

I’ve been running Mint MATE since 2017, good solid OS in my book 👍

Advice: Try to stick with LTS distros (Long Term Support).

The only way I know to harden Linux Mint is using the Debian edition. Using LMDE, you can (unofficial) use Kicksecure to harden the base system. This isnt a great solution since the Linux Mint software is untested with Kicksecure and may/will reduce the security of the overall hardening.

Does Mint have Apparmor installed?

It is default on OpenSUSE. When you add a new application you start apparmor, run your application through its normal use, it “learns” how the system is used by the app, you then apply this as an enforce option or warn option. If the app deviates it gets blocked or warning generated.

Also OpenSUSE has a hardening GUI that looks at your system and configs and lists out all the areas that pass, fail or need attention. It is a great visual tool, and gives explanations/suggestions. Maybe there is Mint package that emulates this. Yast Security Center (see image)

https://documentation.suse.com/sles/15-SP4/html/SLES-all/cha-security-yast-security.html