@AzDev - Thank you for reaching out on Microsoft Q&A Platform.
Updating the information here from comments for broader community usage.
In general number of options do exist for monitoring and alerting of managed instances that can be considered, be it Microsoft cloud native, on-premises products, custom solutions or third party solutions. If you haven't already reviewed , please refer to this blog which summarizes options available to monitor managed instance resources and performance. However the list gets shortened if you are looking for real time and not near real time( example 1 min sampling frequency) doesn't fit your requirement.
Please note that products and options listed in the article, might have additional features added over course of time , request to please research for specific tools accordingly.
Hope this information helps. Please feel free to revert back if you have any further queries. Thank you