This already exists...border agents can require you to unlock your phone and other electronic devices, without a warrant or probable cause. Refusing means facing denial of entry
I know that - it's not the same. Border agents will not say "Hey, we think you have 2 phones, and you brought only one. We'll deny entry and next time bring both."
They also don't say "Hey, this phone you gave me doesn't have any photos. You must have backed them up elsewhere and are hiding them from me. I'm denying entry."
In other words, they don't say "Hey, bring all the photos you ever took."
Yes, and that's bad. "This isn't a problem because it's always been a problem" isn't a defense.
And, we must acknowledge the obvious: such authoritarian rules and requirements rely on benevolence. Meaning, if your leader and border agents are good people, then this isn't a problem.
Well... are they? I say no, so now this is a problem that didn't exist previously.