For anyone wondering, this is what I do personally: for the iPhone, you can have it pair locked (1) with a MacOS (obviously one isn’t accompanied with you during the travel) that way they can’t -even if you were foced to unlock it- they can’t image the OS for further forensics, as that’s usually the case at borders, you wait an hour or two until they copy the image, or worse, planting some malware. This doesn’t work for Android btw.
For laptops, as I mentioned in another comment, using plausible deniability (veracrypt provide such functionality (2)), where you can login to a decoy OS if you were to be forced, keep in mind some deep forensics might give an indication that there’s another OS hidden and encrypted but very hard to do so.
Also, EFF guide from the article below on about the borders (3)
For those wishing to do this, keep in mind you should not then travel with your iPhone AND the device you pair-locked your phone to (your laptop, for example). This may be obvious but is important.
For laptops, as I mentioned in another comment, using plausible deniability (veracrypt provide such functionality (2)), where you can login to a decoy OS if you were to be forced, keep in mind some deep forensics might give an indication that there’s another OS hidden and encrypted but very hard to do so.
Also, EFF guide from the article below on about the borders (3)
(1) https://arkadiyt.com/2019/10/07/pair-locking-your-iphone-wit...
(2) https://veracrypt.eu/en/Plausible%20Deniability.html
(3) https://www.eff.org/files/2018/01/11/digital-privacy-border-...