Import ActiveDirectory schema files into OpenLDAP

I try to add objects of type User (https://docs.microsoft.com/en-us/windows/win32/adschema/c-user) to a OpenLDAP database.

This fails, as the objectClass User is not preinstalled with OpenLDAP and Ubuntu.

The AD schema files are available at
https://docs.microsoft.com/en-us/windows/win32/adschema/active-directory-schema#:~:text=The%20Microsoft%20Active%20Directory%20schema,in%20an%20Active%20Directory%20object

I downloaded the files, and I tried to import them into OpenLDAP but then I get an error message:

# ldapadd -Y EXTERNAL -H ldapi:/// -f AD_DS_Classes__Windows_Server_2016.ldf 
SASL/EXTERNAL authentication started
SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
SASL SSF: 0
adding new entry "CN=Organization,CN=Schema,CN=Configuration,DC=X"
ldap_add: Invalid syntax (21)
    additional info: objectClass: value #1 invalid per syntax

I am brand new to LDAP at all and I do not know how to proceed.

Anybody knows how to get this working?