To-Do List sync via CalDAV

I am using the Gnome To-Do app and want to sync my CalDAV to-do-lists.

My To-Do Lists are safed on an hosted Open Xchange Server (via CalDav) so I could not set it up as a Ubuntu Online Account. I used Evolution to set it up my Account in the evolution-data-server hwich works fine. Sync for CalDAV calenders and to-dos in evolution works, sync for calender with the standalone calender app works, too. CardDAV sync for contacts also works.

But syncing tasks with the standalone to-to app does not work and I dont understand why.

I did some research and found some fairly old bug reports with the similar issues.

• https://bugs.launchpad.net/ubuntu-gnome/+bug/1640180
• https://bugzilla.gnome.org/show_bug.cgi?id=720519
• https://help.nextcloud.com/t/next-cloud-donest-work-properly-with-gnome-todo/25240

So I have to questions. Do you have a working CalDav sync for to-dos (not via Nextcloud etc.) and can you help me fix my setup? If this bug has still not been fixed do you have any suggestions for another to-do-list app which syncs via CalAV?

Thanks for your help :)