What are y'all talking about? Not hard to find this. At PAX West, you could press the Home button on any Switch and it would go to the dev menu. Here is a picture I took of a Super Meat Boy Forever unit that I pressed the home button on:
I even had a developer at the Nindies Arcade whip out a Switch to show me something and boot into this menu. Not exactly a secret or anything, haha.
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Literally just click the Home button on a demo unit at any gaming convention.