Today this is a very relevant issue, because an incredible number of Ukrainians have left Ukraine, and still not everyone knows where they are :) Let's figure it out.
Definition of concepts
Za kordonom are adverbial compounds that must be written separately. It can be replaced by the phrase "outside the country."
Zakordonom (zakordon) is a noun that we write together. It is usually used colloquially to mean foreign countries or foreign countries (abroad) .
You need to learn Ukrainian, but most importantly, don't be afraid to speak it. Remember that it is not important how exactly you pronounce this or that word. The main thing is that it is in Ukrainian 🙂