While the free version of Malwarebytes doesn’t provide "real-time" protection (it won’t stop an infection as it happens), it is the gold standard for cleaning up a computer that is already infected.
Avast offers a massive suite of features for a free product, including a network security scanner and a "Do Not Disturb" mode for gaming. Free Antivirus Software You Can Protect Yourself With
Running a manual scan once a week to catch anything your main antivirus might have missed. A Quick Reality Check While the free version of Malwarebytes doesn’t provide