Based on this old thread :
You need to set up a Linked Service for Azure SQL Database Managed Instance in Synapse:
So start by creating the linked service within your Synapse workspace that targets your Azure SQL Database Managed Instance. This connection facilitates interaction between Synapse and the SQL Database, enhancing your data management capabilities.
How to configure a Spark Pool in Synapse?
Proceed to create a Spark pool within your Synapse workspace. This component specifies the computational resources allocated for Spark sessions, with adjustable parameters like node count, node dimension, and auto-scaling options. Node sizes vary from small to XXLarge, catering to diverse project demands. For tasks necessitating enhanced isolation, the XXXLarge node size offers an Isolated Compute feature.
How to integrate the Spark Pool with Your Synapse Notebook?
Access your Synapse Notebook and head to the Compute section. Under Attached computes, opt for the Synapse Spark pool. This integration allows your notebook to leverage the Spark pool for executing Spark operations on data sources, inclusive of the Azure SQL Database Managed Instance.