Avira does offer 2 additional methods that may work to remove that System Extension. The first one is with the uninstaller and the second is without it.
The other file that still needs removed is com.piriform.ccleaner.CCleanerAgent.plist. In the Finder, choose the Go menu in the menubar and choose Go to Folder. Enter /Library/LaunchDaemons, and you will see that file where you can move it to the trash and empty it. Follow that up with a restart.
Sophos is another difficult to remove piece of software without its uninstaller. You can check here for a removal tool.
https://support.home.sophos.com/hc/en-us/articles/115005499786-Uninstalling-Sophos-Home-on-Mac-computers?source=search
While that is just one of the reasons why we never recommend to install any of these types of software (Cleaners, AntiVirus, VPN), I understand they are heavily marketed as providing security and performance improvements and that is simply not the case. You are not alone and many others fall for their marketing as well and don't realize that these companies intentionally make it difficult to remove their software.
I am not opposed to the suggestion by Owl-53 for the "Nuke" option to set up your device again from a Time Machine backup by only importing your User Account. It can be difficult and time consuming to remove every System Extension you have there, but I am willing to help in any way I can. At his point I will refrain from posting the difficult instruction for removal depending on what you are able to accomplish and if you have reached your goal of removing the icon in your menubar.
