Hello,
I'd recommend checking your permissions. Please see the following troubleshooting guide:
Troubleshoot Azure Migrate projects
https://learn.microsoft.com/en-us/azure/migrate/troubleshoot-project
What Azure permissions are needed?
You need Contributor or Owner permissions in the subscription to create an Azure Migrate project.
Can't create a project
https://learn.microsoft.com/en-us/azure/migrate/troubleshoot-project#cant-create-a-project
If this is helpful please accept answer.