Yeah, that's my position.
If you're paranoid enough to be using GrapheneOS, why would you take it to an airport in the US of all places?
I bought a second hand iPhone for overseas trips, which my daughter promptly stole because she wanted an iPhone, but then i got her old android phone, which was LineageOS-compatible, so that became my travel phone.
The US is known for it's freedoms and protections. It's one of the safest place to take a personal phone.
How do you manage data between your primary and travel-phone?
I _think_ you would need a fresh iCloud account (thus losing access to purchased apps and subscriptions). You also need to manually create fresh social media accounts, copy over contacts, etc.?
Any advice on how to automate this process or is this just a 2-4 hours exercise you do before your trip?