Hello SFF-2954,
Thank you for posting in our Q&A forum.
For Computer Configurations > Preferences > Control Panel Settings > Scheduled Tasks
You could try to use the account "SYSTEM" (NT Authority\System) and then you can select "Run whether user is logged on or not".
After that check if it helps.
Here is a similar thread for your references.
Schedule a Shutdown Task using GPO
https://social.technet.microsoft.com/Forums/en-US/1317f73d-0d78-461a-b0e4-684d32040429/schedule-a-shutdown-task-using-gpo
Hope the information above is helpful.
Best Regards,
Daisy Zhou
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