When access is limited to adding only, using our Calendar functions or Events functions in FileMaker will only return one calendar with VIRTUAL_APP_CALENDAR_UUID as identifier. You can still add events and simply not specify the calendar or use the default one (see Events.defaultCalendarForNewEvents). The calendar is in the virtual source with identifier VIRTUAL_APP_SOURCE_UUID.
If you have an existing solution using our Events functions, please check system preferences to grant full access and everything should continue to work. If you still use older Calendar functions on macOS, please switch to newer Events functions.
Let us know if you have questions.