ConvertKit supports full DMARC compliance.
For DKIM configuration, please visit: https://help.convertkit.com/en/articles/2502558-using-a-verified-domain-for-email-sending
For SPF configuration, please visit: https://help.convertkit.com/en/articles/2502558-using-a-verified-domain-for-email-sending and consult with the vendor's support.