Catalina killed CalDAV reminders

I thought I was careful when installing Catalina to not convert the Reminders database to the new format. But apparently that wasn’t enough. As of yesterday my Reminders won’t sync anymore to a standards compliant CalDAV server. I’m now forced to use either Fantastical or BusyCal. Both expensive applications that I really don’t need, other than for syncing to my server.
It’s a pity to see that Apple is moving away from open standards like CalDAV.
And if anybody knows about a (simple) reminders app that does sync with a CalDAV server and is less expensive than BusyCal and Fantastical, please let me know