Once it's a known feature, analysis finding out about it would be added to commercial forensic tools. Given the first two links, simply hooking up a computer to the unlocked phone would allow Cellebrite to give border guards the information that you are using a hidden partition in a user friendly UI.

For example, documents like this[1] document any features that law enforcement should be aware of.

[1] https://www.swgde.org/wp-content/uploads/2025/09/2025-08-21-...