For any BPMN diagram the canvas is not displayed.
I downloaded the camunda-modeler (again) and started the newly downloaded modeler, the canvas is still not visible.
found where the settings of the camunda-modeler are stored (ubuntu):
Removed the directory <user-home>/.config/camunda-modeler, restarted the modeler and the canvas is back again.
However it would have been nice, if the settings location of the camunda-modeler had been documented in the official camunda-modeler documentation(for all supported platforms)