Ok, I think I got ldap sync (partially) working (once carefully reading 
)
In authenik:
- One needs to use the IP number and port of the provider detail, in my case: ldap://10.5.4.1:20088
- Correct bind and base DN
- DE-select sync groups option (for now)
- Under advanced ldap setting: Object uniqueness field: uid
I can now sync and get the NS8 users in Authentik. Hopefully it is a good start to explore further like correct mappings, groups and other functionality.
HTH