Hi @mark gordon
Based on my searches, SQL Managed Instance offers close to 100% compatibility with the latest SQL Server (Enterprise Edition) database engine. I also found examples of installing the developer edition on an Azure VM: https://www.mssqltips.com/sqlservertip/6620/install-ssrs-reportserver-databases-on-azure-sql-managed-instance/.
I don't know much about Azure SQL Managed Instance, but the version may be a reason. I found in the official documentation that Azure SQL Managed Instance support is mentioned in the new features of SSRS 2019: https://learn.microsoft.com/en-us/sql/reporting-services/what-s-new-in-sql-server-reporting-services-ssrs?view=sql-server-ver15#sql-server-2019-reporting-services. In some articles, it is also possible to host a report server database on Azure SQL Managed Instance using SSRS 2017.
You can refer to these links to view the details and steps to migrate the report server database of SSRS instance to Azure SQL Managed Instance:
Hosting SSRS databases in Azure SQL Managed Instance
Modernizing SSRS And A Step-by-Step Guide to Bringing ReportServer Databases to SQL Managed Instance
Best regards,
Aniya