Certificate-based authentication with Zapp on Mac OS

Hi, I am struggling to get certificate-based authentication working with Zapp (Version 2.1.2.38 but also prior with 2.1.0.190 and before) on Mac OS Catalina. Has anyone similar issues and an idea how to fix? All browser and non browser based apps are working fine with SAML auth but Zapp.

Thanks,
Bernd