If the Azure Migrate assessment is showing that the SQL connection status is "Disconnected", it could indicate a problem with the connection between the Azure Migrate appliance and the on-premises SQL server.
Here are some steps you can take to troubleshoot the issue:
Check that the SQL Server is running and can be accessed from the machine running the Azure Migrate appliance.
Make sure that the SQL Server is configured to allow remote connections. You can do this by opening the SQL Server Configuration Manager on the SQL Server and enabling the "TCP/IP" protocol.
Verify that the SQL Server instance is configured to use the default SQL Server port (1433). If it is using a non-default port, you will need to specify the port number in the connection string.
Check that the SQL Server instance is not blocking incoming connections from the Azure Migrate appliance IP address. You can add the IP address to the SQL Server firewall settings to allow incoming connections.
Ensure that the user account specified in the Azure Migrate appliance has sufficient permissions to connect to and query the SQL Server.
If none of these steps resolve the issue, you may need to check the Azure Migrate logs to see if there are any error messages or contact Microsoft support for further assistance.