Turns out only one small change was necessary for Keycloak with the Quarkus operator: Blank page after clicking Admin Console - #7 by dcrouchelli
Including the port number in the hostname in example-kc.yaml:
hostname: localhost:8443
I still have not learned how to set these KC_* environment variables in the Keycloak container using the Quarkus operator. I have asked StackOverflow: Quarkus Kubernetes operator: how to set environment variables in application container (not operator container)? - Stack Overflow
Thank you!