You can also open the Run command, press Windows key + R then type: appwiz.cpl then hit Enter. If the Start menu is inaccessible after an upgrade, press Windows key + X then click Programs and Features, select your incompatible Antivirus utility then uninstall it.
You can try uninstalling them, then reinstall a compatible version or switch to the built-in Windows Defender. Users have reported being unable to open the Start menu, or the desktop will flicker, antivirus utilities are notorious for this.
Incompatible applications are a common reason why Windows 10 installations might be broken after upgrading.
