An antivirus is mostly just a blacklist of known malware. Sometimes heuristics are used such as 'this piece of software isn't installed on many PCs, and it appears to be doing shady stuff like, monitoring keystrokes or listening to your microphone'. But unless your antivirus is actually sentient there's no way for it to really distinguish between a chat application that listens to your microphone so you can talk to your friends / monitor your keystrokes to know when you've hit the push-to-talk key, and a piece of actual malware that intends to spy on you and blackmail you.
What you have with a package manager is a whitelist of programs that have been selected by your distro maintainers. Is it completely impossible for someone to sneak malware into a distro's repository? No, but its a lot easier to maintain a list of known good software than it is to maintain a list of known bad software. And in that situation your antivirus isn't going to help you anyway, since the people maintaining its malware list aren't going to magically know that something is malware before the distro maintainers do.
So, generally, just using your package manager instead of running random shit you find online is going to be a lot better than any antivirus. With things like Wayland and Flatseal becoming more common we're heading towards a situation where fine-grained per-package permissions will become the standard way distros do things, making antivirus even more unnecessary.
We should have done that a long time ago, as the security model of 'any program you run can do anything you can by default', then blacklist the ones that inevitability abuse that privilege, is completely backwards.
