"white culture" is not a thing
there are no historical examples, or periods of time, or any kind of precedent whatsoever, for a thing called "white culture"
"whiteness" or being "white" is an idea that is only defined by exclusion - i.e. who is not white, is all that defines whiteness
To the ignorant and the dishonest, in their mind, "white culture" is the collective culture of all people with "white skin".
They want to talk about it like this objective thing, but history has proved whiteness is always changing and not some static objective concept.
Does your "white culture" include the Irish? What about Greeks, and Italians? Was the Roman empire white? Was classical Greece white?
If you say yes, it's just an objective fact that those groups were not considered white until within the last 1-2 centuries. So "white culture" isn't so objective, is it?
What about today? Are Albanians white? Are Serbs? Are Croatians? Are Basque people white? Their skin is white, so are they part of this "white culture"?
There is of course Irish culture, English culture, French culture, Italian culture, Scandinavian culture, German culture, Spanish culture, Russian culture, etc. Which of these cultures are "white" and which are not, is ever-changing.
So when you actually understand these concepts of whiteness and "white culture", as they exist in the real world, it becomes obvious why Grimes' tweet is problematic - "white culture" is not a thing and it has never existed.
Now, I'm willing to bet that Grimes is just a well-meaning ignorant normie, and in her mind "white culture" is just the collection of cultures of people with white skin, and that she is not dog-whistling white supremacist virtue signals.