Just to close this topic up. It seems one mayor factor seems to have been that the "worker" in authentik was stuck and therefore did not attempt to connect to process the ldap connection. After it started processing the connection it ran into some python tracebacks because of missing attributes. I could not get the sync to run, but then anyways decided to do it the other way around and use authentik as my primary source of users and connect my Cloudron to authentik instead.
The final switch is still pending however as Cloudron already has an ldap source configured, which I am going to decommission soon.