Following the steps in “Automating installation of Rhino 6” and passing the arguments "LICENSE_METHOD=ZOO","ZOO_SERVER=<my-server>"
to the installer, which seem to be correctly reported in the installation log
[9998:5AA0][2020-09-02T14:33:01]i000: Setting string variable 'ZOO_SERVER' to value '<my-server>'
[9998:5AA0][2020-09-02T14:33:01]i000: Setting string variable 'LICENSE_METHOD' to value 'ZOO'
[9998:A1CC][2020-09-02T14:34:23]i410: Variable: LICENSE_KEY = *****
[9998:A1CC][2020-09-02T14:34:23]i410: Variable: LICENSE_METHOD = ZOO
[9998:A1CC][2020-09-02T14:34:23]i410: Variable: LICENSE_VALIDATION_CODE = *****
[9998:A1CC][2020-09-02T14:34:23]i410: Variable: ZOO_SERVER = <my-server>
After launching rhino I still get this window