I assumed this is more a Nextcloud-topic. I asked the community there ten days ago but got no answer. If somebody here has an idea, I would appreciate that.
I integrated my Nextcloud Contacts into the Contacts app of macOS 12.7.5. This worked fine round about a year. Since a few weeks, macOS is permanently asking for the password. When I do provide it, the password seems to get accepted. But a minute later I am asked again, without an indication of a false entry.
This problem is true only with Contacts. I also synch Email, Calendar, Tasks and Notes. Those services are connected as several different accounts. Only the connection to Contacts is affected.
Logically, a new contact, created on my phone, appears in the cloud but not in macOS.
Remove and then add again your account. First thing to think about on macOS.
I should also warn you that this is a forum about /e/. We can support issues on /e/ devices or software provided by /e/. Our answer risk to be irrelevant, you better ask the nextcloud or apple communities.
Thanks you @VinK3645 for your suggestion. Unfortunately, a new registration of the account is not possible. “account name / password could not be checked” (translated). The same password still works for the stated other accounts.
I am aware, that this is mainly a Nextcloud problem. But as I said: No help from the community there. I will now wright to the staff of Murena.