Windows Defender should be more than good enough for most users. Just make sure to use an adblocker (such as UBlock Origin), only visit HTTPS sites as much as you can (you should see a lock in the corner of the URL bar on most browsers) and ensure you always virus-scan programs you downloaded before running them.

Also, exercise caution on the Internet in general. Never just click "yes" when a program asks for admin permission - make sure you check exactly which program is trying to do it and that the publisher is reasonable. Never exit read-only mode on Office-suite documents unless you know the document is for-sure safe (exiting read-only mode allows macros to run).

Doing all of this, Windows Defender should do fine. I'm assuming 99% of this is common sense for you though, since you've already found your way to the Fediverse!