The issue in this bug is already resolved in upstream Qt.
Your issue is a different issue, i.e., that there is no UI to set default margins. Any settings you make in the print dialog are not intended to be stored as defaults.
The place where you set default settings is using the print-manager KCM, i.e., the Printer tab in Plasma System Settings. But there is no setting for margins there. And of course not for "Force rasterization" which is an Okular-specific setting.
The issue in this bug is already resolved in upstream Qt.
Your issue is a different issue, i.e., that there is no UI to set default margins. Any settings you make in the print dialog are not intended to be stored as defaults.
The place where you set default settings is using the print-manager KCM, i.e., the Printer tab in Plasma System Settings. But there is no setting for margins there. And of course not for "Force rasterization" which is an Okular-specific setting.