Every border on Earth already reserves the right to search your personal effects as thoroughly as they please, without any concept of probable cause being applicable.
If they don't extend that into data located on devices you're carrying across the border, it isn't because they don't reserve the right, but merely because they lack the means or interest.
> Every border on Earth already reserves the right to search your personal effects as thoroughly as they please
You're correct, however this does not mean they all treat you like you should be the most thankful person of Earth for them letting you in and not harassing you endlessly.
The U.S. even requires you to hand over social media passwords in some cases and a lot of personal information before you even get on the plane.
The outright contempt for foreigners is not as common elsewhere.
P.S. And of course, you have borders like between EU countries where you barely even notice you crossed a country border, (as an EU citizen).
If they don't extend that into data located on devices you're carrying across the border, it isn't because they don't reserve the right, but merely because they lack the means or interest.