Avira Security is NOT running on older operating systems like macOS 10.13 High Siera or macOS 10.14 Mojave.
To install Avira Security, you first need to update your operating system to macOS 10.15 Catalina or higher.
If you don’t intend to upgrade your operating system, you can install and use the previous version of Avira Security for Mac.
- Download and install Avira Free Antivirus for Mac.
Further information regarding the configuration is available in the following articles: