The K210 hardware Krux runs on has no wifi.
It has no bluetooth.
And the device is not connected to a computer or phone.
This is completely irrelevant to the discussion.
The only ability the device has to reach the outside world is via QRs displayed on the screen, such as Bitcoin signatures. And Bitcoin signatures are math. If anything on a hardware wallet attempts to change any detail in a transaction, the signature will fail.
Again, irrelevant; Bitcoin signatures are not subliminal-free.