Run script on login *as root* on Catalina
I recommend using crontab.

Open the root user crontab (this will create a new crontab file if you don't have it):

sudo crontab -e

Add you command, with the time you want it to run in front (if you want to do it at a specific time, you can use this handy tool):

@reboot /Users/Shared/Test.sh

Exit and save the file.

That's it! Your command should now run whenever your computer starts up. While this isn't technically the same as on login, it should be enough for almost all intents and purposes.