Hi @Justin_MSCloud,
Welcome to Microsoft Q&A Platform. Thank you for reaching out & hope you are doing well.
Thank you for your patience.
The product team has informed us that 'Flow log capture at "Azure SQL Managed Instance" is not supported. We can only capture flow logs at VMs/VMSS instances.'
Currently, we don’t have support of these below mentioned PAAS services that are integrated into vnet using Subnet delegation just like NSG flow logs.
https://learn.microsoft.com/en-us/azure/network-watcher/nsg-flow-logs-overview#incompatible-services
This information related to 'Vnet flow logs' will be updated in the public documentation soon.
If the above mentioned is unclear, please add a comment below so that we can assist you with the issue.
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Thanks,
Sai Prasanna.