In order to do that, you would need to have your user logged in and the machine unlocked at all times. There is no other way to force the machine to unlock and the user to sign in automatically, other than the cloud trigger in unattended mode.
If you are okay with the possible implications of having your machine exposed at all times, you could modify some settings on it to prevent the user from getting signed out automatically and the machine from sleeping/locking. You could install the Sysinternals Autologon script to make the user login automatically upon bootup (in case the machine restarts due to a Windows update or a power outage). And then if you have a Premium Power Automate license, you could use an API call or an external CMD call to launch the flow. Or Windows Task Scheduler to run it on a schedule.
You would also need to make sure no one logs in to the machine via Remote Desktop Connection, as that would interrupt any flows during runtime, as well as make the user get logged out upon closing the session. So, you would need an alternative, less intrusive (but equally or more secure) way of connecting to the machine, such as TeamViewer, AnyDesk, or similar software.
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