We found examples for granting permissions to a list item using the REST API by email address or SharePoint Group ID. We haven't found an example of how to add an Azure AD security group to a SharePoint list item. Anyone aware if this is possible and what the format would be for the POST HTTP action in the flow to accomplish this? You can manually give direct access to an Azure AD security group using the user interface for the list item permissions.
Here are instructions for applying a specific user or SharePoint group: