Providing opt-out link when sending an email directly from a contacts record
is_opt_out isn't a link, it's the privacy preference checkbox on the contact record.
I don't believe the bulk mailing link tokens are available in this context, since you're not sending bulk mail.
But you can use the checksum token to include a link to a contact profile you set up. https://docs.civicrm.org/user/en/latest/common-workflows/tokens-and-mail-merge/#checksum