Hi Mario,
Objo currently uses its own print dialogs with a shared printing layer across macOS, Windows and Linux. Pages are rendered to PDF and handed to the operating system, so the OS still handles the actual printing.
The limitation is that Objo's dialogs only expose the basic settings. Paper tray selection and colour versus black-and-white printing aren't currently available through PrinterSetup.
I've looked into this and logged a feature request for native print dialogs on all three desktop platforms. I've also written an implementation plan. The intention is to expose the options provided by the selected printer and driver while keeping the existing Objo printing API.
It needs more than a dialog replacement because those settings must be preserved through rendering and submission. I don't have a release date for it yet.
For now, exporting with PrintJob.SavePDF and printing from a PDF viewer that exposes those options is the workaround.