Hi Gilles,
Greetings form Syncfusion Support.
Q1: We suggest you to refer the below UG document links to know more about ICS Import and ICS export.
Q2: How to display these appointments as a all day appointment?
Please refer the ICS format for all day events from below.
BEGIN:VEVENT
LOCATION:
SUMMARY:All-Day event
UID:d95612bb-8a59-87a0-c80f-a1b2a6eba247
DTSTART;VALUE=DATE:20190109
DTEND;VALUE=DATE:20190110
DESCRIPTION:
ISREADONLY:false
END:VEVENT
Q3: How to make the appointment read-only ?
Please refer the ICS format for read only events from below.
BEGIN:VEVENT
LOCATION:
SUMMARY:Read only event
UID:bb9a2590-d4fa-8016-3919-63b4b5e8907e
DTSTART:20190108T100000
DTEND:20190108T110000
DESCRIPTION:
ISREADONLY:true
END:VEVENT
Also we suggest you to refer below UG to know more about read only and all day
Regards,
Vinitha