To run a PAD flow in unattended mode premium license is required.
But, if you run a flow manually/attended mode and lock the system then flow will run. For example, if you are running a flow which takes 10 mins to prepare a report.
Here is a sample flow for your reference. I ran a flow and immediately locked the system. After a minute, i re-login and flow was executed successfully.

If I have answered your question, please mark my post as Solved.
If you like my response, please give it a Thumbs Up.
Regards
Kaif