UPDATE: See other comment
Yes, we are receiving the same error message with Nextcloud within our Univention environment.
However, we started receiving the same error message a full month ago, and haven’t been able to log-in since.
It was not a new installation in our case–it just suddenly broke.
It could be the case that Let’s Encrypt was handling certificates for the LDAP server–and we moved off Let’s Encrypt to an on-prem certificate authority–but we still haven’t found where all of this is configured. If a certificate has expired, we can’t find it. (It was working for months after we moved off Let’s Encrypt, though…, so it wasn’t just that.)
I even tried setting this in the configuration files to turn off usage of TLS for LDAP (/etc/univention/templates/files/etc/ldap/ldap.conf as well as /etc/ldap/ldap.conf) with no success:
TLS_REQCERT never
I would be very interested to know what is causing this problem.