Ok, I think I have found a solution.
In the Settings menu link you must deactivate “Restrict the iCal menu entry (see important information in the tooltip!)”.
If I have activated this setting, selected the corresponding categories, then saved them, then deactivated the setting "Restrict the iCal menu entry (see important information in the tooltip!)" - then on the menu link "Events-ical Export" page the previously selected categories will be displayed after deactivating "All Categories".
If I export iCAL calendar entries with "all categories", then everything, EVERYTHING, is exported.
If I deactivate "all categories" - as mentioned above - the categories previously shown in the settings of the menu link are displayed to me, and only these are exported to ical Google Export.
So if users export a calendar, they must deactivate "all categories", then only the corresponding preset events will be exported.