Harmony Remote and Apple TV - "start position"
My ATV4 has a "Menu" button (upper left button, below touchpad).  Touching it from anywhere on the homepage takes me to the home screen, and selects the upper-left icon (Settings, for me).

But, if you're inside a "folder" on the home screen, or inside an app, it usually takes 2 clicks to get back to that top-left tile.

Before you say, "just program 2 clicks every time", when you do that from the home screen itself (not in a folder or app), that launches the screensaver.  You'd need to press Menu again to get out of the screensaver, but 3 clicks would send the other scenarios into the screensaver...

There is no sure-fire way to get to the top-left tile, and then to your Netflix app.  Unless you're willing to use the reboot function, which is available in the Harmony setup for ATV, but that kind of defeats the purpose of getting to Netflix quickly...