Google says the Pixel 4's Motion Sense features will only be available in a handful of countries due to regulations surrounding the underlying Soli radar technology. Since it could potentially interfere with navigation systems and military equipment, the company is careful to make sure it won't work anywhere where it's not approved. Thus, Soli will disable itself when you enter unsupported regions.
Two members of the Soli team have confirmed to us that the Pixel 4 will determine if you're in a country where the radar feature is not supported using cellular triangulation and then deactivate itself.
We don't know if you could get around this if you keep your Pixel on airplane mode, but then you could as well leave it at home. Either way, this means that even if you import your Pixel 4 from a location that supports Motion Sense, it'll deactivate itself as soon as you turn it on.