If I'm understanding this sentence correctly, you are saying that modern state could exist without discriminating people regarding of their ethnicity.

No, I said that they state that this is what they do. I said that this was their claim. I didn't claim that this was correct.

their [sic] is no scientific differences between nations, ethnicities or races.

That's true. But the concept doesn't have to be scientifically valid to be a reason for discrimination or privilege. Jim Crow and the Nuremberg race laws simply referred to what was considered race science at the time.

Nations are social construct,

True, but that doesn't negate anything

usually based on genocide.

that's sure as shit not how states present themselves, though.

Let's take Germany as an example: There is a high percentage of german mitizens of Turkish decent who have been living in Germany for generations. Many of those people have German citizenship. Sure, there's still racist discrimination going on, but these people are german, as far as the state is concerned. It's actually illegal in Germany to discriminate people based on ethnicity, so technically, only the passport should be taken into consideration.

The meme is mainly based on how Germany presents itself.