Windows Defender is the default anti virus solution on Windows by now and it is good. But no anti virus is perfect. It is a good idea to have a backup strategy if you plan on having any important data on your PC. In case of encryption malware and hardware problems.

Phishing is also very problematic practice that the anti virus can’t protect you from and even experts can fall into the traps. So you have to be careful with your account credentials.

Don’t disable Windows updates or postpone them indefinitely (though windows makes that harder to do anyways). Also be aware that your PC might need firmware updates too to stay secure. It depends on the manufacturer of your hardware how and if these are provided and how you install them.

Lastly I can recommend using Firefox with uBlock Origin. Using an ad blocker can help you stay safer and Firefox has very good support for them.