Does a Mac actually need antivirus?

Agree. The one setting worth checking: System Settings > General > Software Update, click the info button next to automatic updates and make sure Install Security Responses and system files is on. That's how XProtect gets its updates, and some people turn it off with the rest. Only time I'd bother with a scanner is if you pass a lot of files on to Windows users, it can catch Windows malware that wouldn't hurt the Mac but would hurt them.

For most people, no. macOS already has XProtect and Gatekeeper built in, and they update quietly in the background. What actually gets people on a Mac is fake installers, browser extensions full of adware, and phishing, and an antivirus doesn't do much about the last one. Keep it updated and only install from the App Store or the developer's own site.