The Ai below seems to be complicating the process.
If you want to add a program to the Start-Up tab in Task Manager, these are the steps.
Create a new Desktop icon for the program
Open File Explorer.
Paste this into the address bar in File Explorer and press Enter.
shell:startup
Then drag the new Desktop icon you created into the resulting folder.
That's it, that program should instantly appear on the Start-Up tab in Task Manager