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You cannot move the Azure SQL managed Instance from one tenant to another tenant. Please refer the below link to see the resources that were supported for cross tenant migration.
Please refer to the below Accepted Answer thread that might help you:
https://learn.microsoft.com/en-us/answers/questions/367332/azure-sql-managed-instance-migration
Hope this helps. Do let us know if you have any further queries. If this answers your query, do click Accept Answer
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