Hi @AnonUser,
It looks like someone asked this same question here.
As shared in that post, here is the guide for enabling NSG Flow logging.
You would turn on diagnostics logs on all Network Security Groups. To do this, go to Monitoring > select Diagnostics logs > select "Turn on diagnostics."
https://learn.microsoft.com/en-us/azure/virtual-network/virtual-network-nsg-manage-log
Then collect logs for sentinel ("How can I collect from a supported Azure source?"):
Let me know if this is what you are looking for or if you need additional information.