To answer your questions:
Thank you that indeed helps me to understand your configuration a little bit better. I was confused how Outlook/CalDAVSynchronizer should work together with an Android device,
but this makes the picture a little bit clearer.
If Nextcloud is used, can you please also tell us the Nextcloud version being used?
I access my details via Firefox browser. I do not see anywhere a statement which version of Nextcloud is being used
The version number is usually been displayed under Settings > Management > Overview. If you’re not able to access this menu entry you can right click on a Nextcloud page, select View source code of the page and search for “versionstring”.
Yes, in Dutch it is called an ‘Agenda’, but indeed I mean ‘Calendar’. So my Calendar in the browser has the option to create a new ‘Calendar group’.
Ok, that was my assumption too As I already wrote Nextcloud doesn’t have an option to create calendar groups. You can only “Create a new calendar” or “Assign a category to an event”. On your screenshot I cannot see this option either.
Exactly. And in my newly created Calendar group: ‘Zakelijk’ (‘Business’).
To be honest, based on your screenshot you haven’t created a contact group but a new calendar.
P.S.: I see that a device with DAVdroid 2.6.3-x5 is connecting with the website where my Calendar items are. I presume that is my Samsung S7. So this is using DAVdroid 2.6.3-x5.
Ok, that’s fine. Open DAVx5, select CALDAV and then press the reload button in the lower right corner to reload the list of available calendars. Your newly created business calendar should be shown and you have to tick it to get it synchronized with your mobile phone.