Relevant20 Is it possible for the authorities to get my Data, for example via Cellebrite?
As far as I know, Cellebrite's capabilities haven't changed recently, so the answer would be probably not. That said, nobody can say with 100% certainty that a device can't or won't be broken into.
Also, you used Cellebrite as an example. It's entirely possible "authorities" where you live or are traveling to have an exploit that we're not aware of (but GrapheneOS does have protections against unknown vulnerabilities, so you're still far better off with GrapheneOS than with some other OS).
Nobody can say for certain yes or no to your question because there's a lot of things to consider, like your setup, whether your device is up to date, certain settings, etc. But if you keep your device up to date and if you're smart about how you use and set up your device, it'll be much, much harder for malicious people to get access to your device and the data on it.