On https://forums.bitfire.at/category/4/davx there is a link named “DAVx⁵ Manual: TLS / Supported Ciphers” with target (URL) https://www.x5.com/manual/security/
That domain name does not resolve. What is probably meant is https://www.davx5.com/manual/security/
Oh, but it was indeed a glitch by Google Contacts !
I’ve uninstalled the app and reinstalled it, and now all works well :-))
Thanks for making me check and for your quick reply.
Thx. for the APK. After installing it, it works as expected. Thx for the fast Fix.