It would appear that Windows/System32/Group Policy is an empty folder, so no Machine/Scripts/Startup is found, unfortunately.-Techno Grub
The directory structure is created when an entry is input via Group Policy Editor. Group Policy directory is read-only by default anyway.
You just need to go to the appropriate entry in the editor and select a cmd/PowerShell file from anywhere, it doesn't need to reside in Windows/System32/Group Policy/Machine/Scripts/Startup ... but I couldn't get it to run.
It's been a hectic week for me but I'm still trying to find time to try some potential solutions.-skwire
Tried using Task Scheduler set as
Run at startup both as myself with highest privileges and as LOCAL SERVICE with highest privileges, still didn't do anything. Not even attempted according to the task history.
I'll try it later today with it also writing a marker file with the time inside just so I can see if it runs at all in either situation.
ADDENDUM: OK, got it to run at startup and according to the Task History it ran while the Lock Screen was being displayed but it didn't interact with the screen.
The task was apparently started 20 seconds after the Lock Screen appeared and I also had a 20 second delay, Task shows as completing successfully.
Task was set to SYSTEM user.
Now have to try specifically directing the keypress to the winlogon.exe process, might need to do this in AHK/AutoIT/etc as a compiled program.
Was testing this on my laptop and forgot to turn off
Start the task only if the computer is on AC power for initial test ...

Following ran but didn't interact either:
(New-Object -ComObject WScript.Shell).AppActivate((get-process winlogon).MainWindowTitle)
(New-Object -ComObject wscript.shell).SendKeys('{UP}')