> You comply and enter "a" password. The device shows contents. You did what you were asked to do.

No, you did something fake to avoid doing what you were asked to do.

> If there is no way for the government to prove that you entered a decoy password that shows decoy contents, you are in the clear.

But there are very effective ways to find hidden encrypted volumes on devices. And then you’ll be asked to decrypt those too, and then what?

This sort of thing is already table stakes for CSAM prosecutions, for example. Law enforcement can read the same blog posts and know as much about technology as you do. Especially if we are hypothesizing an advertised feature of a commercial OS!