Hi Jens,
Thank you for contacting Syncfusion support.
Based on the provided information your requirement, "Is it possible to restrict it render in all day appointment panel exclusively?”. As per the calendar implementation, the appointment that have more than 24 hours will be render in all day appointment panel exclusively in day, week and work week views, it is the current behavior of the flutter calendar.
We hope that this helps you. Please let us know if you need further assistance.
Regards,
Muthulakshmi K