You're encountering a known limitation with Free Trial subscriptions in Azure. The error you're seeing means your subscription is blocked from creating required resources like SQL Database servers in those regions a common restriction for Free Trial and some sponsored or limited subscriptions.
Code: SqlServerRegionDoesNotAllowProvisioning
Message: Location '<region>' is not accepting creation of new Windows Azure SQL Database servers for the subscription '<subscription-id>' at this time.
As @Nandan Hegde mentioned
You can try creating a logical SQL server in a region different from those you've already attempted. If the SQL server is successfully created, then try deploying the Synapse workspace in the same region.
The most reliable solution is to upgrade your Azure subscription to Pay-As-You-Go. You can do this by clicking the “Upgrade” option in your subscription settings. This change retains your free credits while removing many of the restrictions associated with the free trial.
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