I co-wrote a border search guide for EFF some years ago. I was very interested in finding clever technical approaches but I later ended up feeling that I hadn't given enough thought to the overall threat model questions (even though the guide did address them, perhaps even somewhat usefully). The big picture problem is that the agents performing the searches have an enormous amount of power in terms of potentially se…
So I guess what you really want is a duress PIN that loads into a fake innocent profile.
And using encryption will only make you more suspicious, and may be a reason to get jail time until the situation is "cleared up" one way or another (e.g. by getting even more jail time).
Only a second phone works, if you can make it seem like a device you're actually using (though also not a silver bullet as e.g. a lot of messenger metadata is available to governments and border control can physically coerce you to log in to your real accounts)