So I found a form post about using installing ClamAV with a Slackbuild https://lime-technology.com/forums/topic/12548-anti-virus-scanning-of-backed-up-files-within-unraid/ and read through the following wikipage: https://lime-technology.com/wiki/Methods_of_user_customization#About_Linux_Packages. But they both seem quite old. Is there anything I should know before trying to install the Slack build contained in the page below on Unraid v6.5: https://slackbuilds.org/repository/14.2/system/clamav/ ?

You are referring to very outdated and incompatible links. With unRAID 6 applications are installed using docker containers.

 

If you haven't done yet, go and install the Community Applications (CA) plugin. With this plugin you have the possibility to install applications right from the GUI.