Catalina > Reminders > don't sync anymore > certificate problem?


I am not new here (job account), only a new account for use at home during vacation.
Read all possible solutions at Nextcloud, Github and Apple forums but can’t get it working.

‘Old’ story I know, but what I did:

  • Upgrade Mojave to Catalina (yes, I wait always a half year to do upgrades out of safety)
  • Reminders never asked to update the database.
  • Upgrade Nextcloud 17 to 18 (later version)

What’s the problem:

  • All went fine except Reminders do not sync anymore.

What I have researched:

What I want to ask:

  • How to check if the Reminder database update was done yes or no?
  • A step by step guide how to install the certificate?
  • If that’s not what I need; other tip and tricks.

Kind regards