Everyone has different DNA and nobody refutes that, but the lines at which race are defined are completly arbitrary. Are you considered black if you have 50% sub Saharan African DNA? Most would say yes. Are you black at 25%? How about at 5 or 10%? The slew of different answers is a clue that race is just a social construct borne of perception rather than hard fact.
Similarly, a lot of groups that are considered “white” today would not have been in the slightest if you were to go back 100+ years. The Irish, Italians, Greeks, among others were not considered white until more recently than you might believe.
Thats the crux of it, race is only truly defined by these arbitrary lines in the sand that people draw, and these lines are different for different groups and individuals. Race is only real because people perceive it to be. We could divide up society based on hair color or if your ear lobes hang or are directly connected to your head and it would make just as much sense, which is to say not much.
Edit: I might add that there’s more genetic diversity in sub Saharan Africa than anywhere else in the world but they all get lumped together as black because “skin dark”. It’s stupid when you examine it.