[lovich]

That is highly dependent on the law. For example the United States will prosecute citizens that have sex with child prostitutes in other countries, even if that is where they reside full time. Other laws like the GPDR you mentioned are dependent on the physical location of the activity

[jkaplowitz]

In both the UK and the US, the legal systems have a strong presumption against that interpretation for laws which don't say otherwise.

The example you give is one where Congress made clear they intended it to apply to citizens abroad, so the courts honor that.

(As for the US Constitution, it is held to protect the rights of US citizens abroad in relation to the US government, to the extent the US government knows or should know of their citizenship.)