Hello
Thank you for your question and reaching out.
There can only be one account policy per domain for domain accounts. The default domain policy, which is enforced by the domain controllers that make up the domain, or a new policy linked to the domain's root that takes precedence over it must define the account policy.
It is not necessary to directly set the password policy to the DC's OU. I strongly advise setting the GPO in the Default Domain Policy because it MUST be linked at the domain level.
--If the reply is helpful, please Upvote and Accept as answer--