Hi Tony,
Welcome to Microsoft Community.
Unfortunately, you won't be able to install some third-party antivirus software on a Windows 11 Arm-based PC—unless it's made or updated for an Arm-based PC. However, Windows Security helps keep you safe for the supported lifetime of your Windows 11 device.
Windows Arm-based PCs FAQ - Microsoft Support Your SincerelyHahn. W - MSFT | Microsoft Community Support Specialist