Hi @馬場 勇真 ,
Thanks for reaching out.
I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this! Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others", I'll repost your solution in case you'd like to "Accept" the answer.
Issue: How to delete Azure AD DS, canceled the deployment job while deploying Azure AD DS, however, the status of Azure AD DS is still showing progress.
Solution: There seems to be some background operations going on which need to complete before deletion. Once the status will be complete/failed, you can delete the Azure AD DS.