Best practices for Power Automate with service account

CSRPhoto you misunderstood it. Each flow needs a license: either the flow owner has to be licensed (per user license), or the flow itself (per flow license). Then your flow can run many times within the limits detailed at https://learn.microsoft.com/en-us/power-automate/limits-and-config.

The 5 licenses mentioned in this discussion is about the minimum quantity of "Power Automate per flow" license that you can order at a time. You can order just one license but 5 as a minimum. So even if you have only one flow to license, you still need to buy 5 licenses. 1 license you will use on your flow and the 4 left will be unused until you need them