Soheil Bakhshi digs into the fine print:
If you are evaluating Microsoft Fabric and do not currently own a Premium Capacity, chances are you’re using Microsoft Fabric Trial Capacities. All Power BI users within an organisation or specific security groups given the rights can opt into Fabric Trial Capacities. Therefore, you may already have several Trial Fabric Capacities in your tenant. Your Fabric Administrators can specifically control who can opt into the Fabric Trial capacities within the Fabric Admin Portal, on the Help and support settings section, and enabling the Users can try Microsoft Fabric paid features setting as shown in the following image:
Read on for a lot more detail, including several common issues you might find along the way.