At this moment, a domain can't be linked (Link domains) to an identity provider directory until at least one Atlassian Account from that domain is claimed.

If the domain is inspected using the browser developer tools, it will show up as:

• "verified": false
• "status": "VERIFIED_UNCLAIMED"

[
    {
        "domain": "abc.com,
        "verified": false,
        "timestamp": "<date-of-verification>",
        "status": "VERIFIED_UNCLAIMED",
        "verificationType": "dns",
        "unclaimedAccountsQuantity": null    }
]

During the claiming process, the domain moves from the status VERIFIED_UNCLAIMED to VERIFIED and is linked to the local directory by default.

After that, it can be linked to a different directory. 

Suggestion:

Allow a domain to be linked to an external directory without requiring this extra step. 

Workaround:

It's necessary to claim the accounts as mentioned in the following documentation:

• Claim accounts

There is no need to claim all the accounts, just one is enough. For that, create a file containing a single user from the domain and save it with the extension .csv.

With the file ready, it's possible to manually claim that single user using the file: