@宏 猪飼 Thanks for reaching out. From the description i understand you were able to create health data services workspace successfully but unable to create fhir service within it could you please confirm? If yes, please ensure that you have the necessary permissions "FHIR Data Contributor" to create FHIR resources you can check your permissions by going to the Access Control (IAM) blade in the Azure portal.
do let me know incase of further queries, I would be happy to assist you.