The Avira support pages seem to indicate there is an uninstall tool located in /Applications/Utilities/Avira-Uninstall.app/Contents/MacOS/Avira-Uninstall and that you may need to run this from Terminal instead of clicking the App in the /Applications/Utilities directory. I recommend not running this tool in the GUI but from Terminal manually as below: xattr -dr ~/Downloads/

I've analyzed the script and it doesn't do anything it is not supposed to be doing. You'll need to allow the script to run and then execute it in Terminal via the sudo (Super User Do) command. The Avira support site provides a script you can download, decompress and run but the file will be initially blocked as it's from an Unidentified Developer. Especially those that use kernel system extensions. It is not uncommon to brick your Mac when upgrading the operating system with an incompatible security tool. For future reference, if you install security tools you need to take note and verify they are compatible before you upgrade the operating system. I suspect you ran into trouble because you installed this prior to upgrading to Catalina. Software with sloppy packaging and removal. The expensive security tools were insane.

Avira uninstall tool mac