The whole (mistaken) belief that Linux and macOS didn't require AV was based on the execute bit being present, something Microsoft fixed back in XP by making downloaded files as such and preventing them from being opened trivially.

If you have code execution, you can attack the OS.

Indeed, when one installs dependencies all over the Internet, or even better, key projects use "curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh" as default suggestion on how to install them, attackers have the work done for them.