This page of the application settings dialog contains options related to the interactive viewports of the OVITO.
OVITO restricts the camera rotation in the viewports such that one of the Cartesian coordinate axes always remains vertical. This selects which of the three axes that is. Default: Z-axis.
This option restricts the camera rotation to a 180° range such that the vertical axis always points upward, i.e., it prevents the camera from turning upside down.
This option selects between the default dark viewport background and a white background.