The Error: your flow could not turn on cannot be activated because an Unattended RPA add-on is required to enable this flow.
Go to power automate admin center https://admin.powerplatform.microsoft.com/analytics/flow
On the left menu you have resources and select from the dropdown capacity
Once there scroll down to add-ons
click manage and assign the RPA licence that you have purchased to the same environment that your power automate runs on.
Easy when you know hey :-)