Can you elaborate more on that? What app does it or how to do it? Any good link to some step by step guide? I think it is useless, because they do forensics if they find a clear device and that looks even more suspicious than having your normal stuff there minus the sensitive stuff you don´t want anybody to see. I would suggest to save that sensitive stuff to a private safe and encrypted cloud until you are ready to sync it back to your phone or laptop once you arrive at your destination. There is one country on earth where you can expect this more than anywhere else, the USA.
Get Vera crypt with a hidden container and make sure you only use iphones. When going through security disable face id by the quick buttons
https://www.macworld.com/article/23...etly-disable-face-id-on-the-iphone-x.html/amp
The of course you become rather forgetful by actually complying with an order to give the password - which you will give as it will probably be enshrined in law or being a court order - but it turns out to be wrong so no one can have access to the device anyMore
Ofcourse you can use encrypted cloud storage not to have anything local - or use an rdp server etc etc
Depends on the country you're entering, countries you've been to and whether you're a person of interest for any investigations in your destination or closely related territories. You're unlikely to get searched without being of specific interest. It's too much effort to search every phone coming through.