Despite what you may have heard, every major class of operating system—including both Linux and Android (which is a mobile-optimized Linux fork)—is susceptible to viruses.  And although Windows includes a built-in tool to conduct basic scanning and firewall management, users should install a dedicated solution.
Most antiviruses are multi-faceted programs that provide protection against a wide variety of cybersecurity threats—and come with clever built-in automation (like turning on a VPN when an online banking website is accessed) designed to keep their users safe. Some browsers include built-in phishing protection, but in most cases, these don’t compare to software offered by professionals.
Use an antivirus—it’s a small investment in your privacy and the health of your computer.