Occasionally macOS may cause the corruption of AdGuard's Network Extension module, making it unable to use the app. In this case you should follow one of these instructions, based on your OS version.
If you have problems launching AdGuard for Mac on Big Sur and Monterey operating systems, please use this instruction:
If you have problems launching AdGuard for Mac on Sierra, Mojave and Catalina operating systems, please use this instruction:
ls -@lOae /private/var/db/KernelExtensionManagement.
restrictedflag is not present (like on the screenshot).
sudo chflags restricted /private/var/db/KernelExtensionManagement.
csrutil enable-> Enter administrator password -> Reboot your Mac.