Countries like China and Japan are de facto ethnostates. There's also countries with religious majorities like Saudi Arabia, Iran, Pakistan, and India, many of which are associated with an ethnicity. Saudi Arabia is named after the Arabs. You could make the argument that many European states have dominant ethnic groups like the French, though they are nominally secular nations.

The biggest cosmopolitan countries are the United States and Brazil if I remember correctly. Maybe Canada too. Europe is moving in that direction. Countries that have a diverse citizenry are more of an exception though. Not that I disagree with your probable view that we should all live in diverse secular democracies, I just think your claim that almost none of the world is ethnostates is somewhat suspect.

I agree with the idea that Israel would ideally be a single secular state, but navigating that transition while preserving it as the safest place the Jews of the world can go would be an enormous challenge. The situation sucks and resists simple answers.