If you’re using a Run Flow-initiated flow and need to verify whether the user has a specific role (such as the Key User role), you can use the following steps to check if this role is assigned to the user:

The user is identified based on the email address found in the header using:
triggerOutputs()?['headers']?['x-ms-user-id']

The corresponding FetchXML will be:

Cheers!
Elowy.