Hello everyone. We have got the same issue on BigSur. I would like to join this thread and receive any reply from Apple Support :)

Thank you so much for full answer. Yes, we are distributing our application using Developer ID certificate with notarization. PKG passed notarization process successfully. We have solved the problem - 3rd party vendor confirmed that it was a false positive decision from their side. Right now the problem has beed solved. Thanks for your help 🙏

About the links - I got it 🙏. Thank you Regarding technical question - my question is incorrect, or this vulnerability doesn't related to Apps or it's a secret by Apple)? Right now it doesn't totally clear, if you can elaborate more I'll really appreciate it

Thanks a lot for your explanation and all answers. I got it - so only one way to avoid Blocked System Extension popup it distribute application only via MDM - company admin should install app using MDM system and whitelist required system extension. Now it's clear. 🤝