System extension blocked on MacOS High Sierra 10.13.6

Hi everyone,
I authorized once a system extension of Avast on Mac OS High Sierra 10.13.6 back in October 2021. When I restarted the computer on the next day, Avast asked again to authorize the extension and I had 5 windows with the “error text”. The problem is: when I open the system preferences, there is no button to click on to authorize the extensions. And the windows keep being there, there is no possibility to close them. I tried to deinstall and reinstall completely the antivirus avast (free version) but it didn’t help.
Good to know: I also have the avast VPN.

Can someone help me? I want to have the “Authorize” button :slight_smile:

Best regards