The previous Avira security solution (Avira Antivirus for Mac) is not compatible with macOS 11.0 Big Sur. If you still have the previous Avira version installed on macOS 11.0 Big Sur you will receive a “System Extension Blocked” message.
Note
In this case uninstall the existing Avira installation and install the current Avira Free Security for Mac.
More information about the installation is available in this article.