How can I hide KM when opening from boot, automatically.
How about this? It seems to work for me. I tested it only once. I'm not sure if I understand your environment.
But I have a question: why? Did you know you can launch the Engine without launching the editor? Why would you want the editor launched if you want it immediately minimized? Why not just launch the Engine instead of the Editor/Engine?
Minimize KM at launch.kmmacros (2.9 KB)
The Keyboard Maestro editor should not generally be launched on boot.
Open your System Preferences, Users & Groups, Login Items, and remove any entries relating to Keyboard Maestro from there.
Then in Keyboard Maestro, select the Launch Engine at Login from the preferences (which will add the Keyboard Maestro Engine to the Login Items above).
On boot, the Keyboard Maestro Engine will run, but the Keyboard Maestro editor itself will not.