Rie Merritt breaks out the toolbox:
Azure SQL Managed Instance provides options within and outside Azure portal for troubleshooting and optimizing performance. Within the portal, you can leverage automatic tuning and Intelligent Insights. Outside of the Azure Portal, you can take advantage of the capabilities that are already in the database engine, such as query store and dynamic management views (DMV). In addition, Microsoft offers several monitoring options that are in preview: Azure SQL Insights inside Azure Monitor, which requires an agent on a VM you own, Azure SQL Analytics, and Azure diagnostic telemetry.
Automatic tuning in SQL Managed Instance supports FORCE LAST GOOD PLAN, which identifies queries using an execution plan that is slower than the previous good plan. It forces queries to use the last known good execution plan. Since the system automatically monitors the workload performance, in case of changing workloads, the system dynamically adjusts to force the best performing query execution plan.
Many of the things Rie describes are also available on-premises, though Azure SQL Analytics is only available in Azure SQL DB and Azure SQL MI, as of the time of this post.