Yes ADSI as linked server is not well documented. It works well for basic queries: no updates. You need a service AD account and add this as any linked server in SQLSERVER: you can sp_addlinkedserver ... I do not remember the syntax OR use EM to add linked server. After which query from this like from linked server. Something similar:

-- Add the linked server via SQL
sp_addlinkedserver 'ADSI', 'Active Directory Service Interfaces', 'ADSDSOObject', 'adsdatasource'
EXEC sp_addlinkedsrvlogin 'ADSI', 'false'
 

--Query 

SELECT * FROM OpenQuery(

    ADSI,
    'select
       cn,
       sn,
       instanceType,
       primaryGroupID,
       whenCreated,
       whenChanged,
      
       sAMAccountName,
       sAMAccountType,
      
       objectCategory,
      
       givenName,
       distinguishedName,
       displayName,
       name,
       telephoneNumber,
       mail,

       userPrincipalName,
       userAccountControl

      FROM ''LDAP://YourAdDomain/DC=...'' where objectClass = ''User''')

I could get the above working. Remember this brings up only first 1000 records. To test if a single account is valid, this works