Thank you in Android 6 its also in at Android Settings / Accounts / More (⋮) / Auto-sync data. I changed it and will test in the evening. The DAVdroid JB Workaround will be deleted too.
The authentication by client certificates has been funded and successfully tested by the computer emergency response team of the Government of the Grand Duchy of Luxembourg – https://www.govcert.lu/en/
Thank you very much
hotfix: synchronization of calendars when event colors are disabled works again