@Sushmita Parajuli Thank you for reaching out to Microsoft Q&A, apologize for any inconvenience caused on this.
Based on the shared information, I have looked the backend logs and get to know that creation of static webapp failed while staticwebapp is trying to add the workflow.yml in the azure deVops repo and also you might not have written permissions on that repo.
Could you please check whether you have write permissions on that repo and re-try the creation of static webapp.
Feel free to reach back to me if you have any further questions on this.