Root certificate not accepted

To prevent issues with the self-signed-certificates on my Mac, I installed the ucs-root-ca.crt into the system keychain on my mac. But I still have an issue with the certificate, because of the wrong standard. Message on my Mac (sorry, it’s in german)

Zertifikat entspricht nicht dem Standard

I’m not sure, but maybe it’s because of this.

How could I create a root certificate the matches these requirements?