That is of course all true in the rapid times of change of mass migration, wars, redrawing of artificial nation borders.

However, genetic traits and cultures and languages change much more slowly.

Even the Croats view themselves as Croats or Adriatics or Zadarians (based on their city of dwelling) and not as "Yugoslavians" or any other artificial definition that the current rulers happen to place on them.

The same for Lappish people (Sami) and so forth.

Yes, cultures do and have mixed, but now we are (again) living in the times of WEAPONIZED migration and the ensuing cultural, economic, linguistic and tribal warfare that results from that.

Just "giving in" to whatever war immigration op currently happens to be active in your country in your lifetime is not something you have to do.

You can still retain your culture, your heritage and life, but not always WITHIN the country that under attack.

So, choose wisely.