I have a friend who is a peace negotiator in the balkans for 20 years. He has lots of amusing (to my horrifying) stories of cat and mouse interrogations with the FSB etc as he travels between Moscow, Kyiv and the West. He uses threema and signal for most diplomatic conversations, but when he travels he only carries burner phones.

If you don't trust a government, ensure you aren't carrying any information you don't want to give up before entering their borders where you will be under their power.