I wouldn't put this in the same category as having a parent who is pro Brexit, pro Trump etc. I think this is a step further. My father denies the existence of the uyghur genocide in China, he believes the CCP propaganda that Urumqi is a 'rich city' and that the concentration camps are just camps for terrorists (like Guantanamo Bay). I challenged this on my last visit home and then he completely switched tack and said, he didn't care what happens in the camps, China is going to rule the world etc etc etc. And they would be the new superpower and defeat america.
I think this is also more emotional for me, because my DH is Jewish (and I also converted to Judaism). As a Jewish person, it is really awful to hear someone else (particularly your own father) just casually write off the extermination of a whole people. For my father, the bigger injustice (compared to genocide) was the sacking of the Old Summer Palace in 1860 when the Summer Palace was sacked and looted by Allied forces. Btw my father wasn't born in China and neither was his father. He doesn't even speak Mandarin fluently. He has visited China less than 5 times in his life. His grandfather (my great grandfather) immigrated to SE Asia in the early 1900s, which is around the same time my DH's great grandparents arrived from Russia/Poland. We have no contact with any family in China. So him supporting the CCP cos of his ethnicity makes just about as much sense as my DH supporting the Law and Justice Party in Poland/Putin. Maybe its because he does this to feel a connection to his roots while I have no need to as a fluent Mandarin speaker, I don't need to support a despotic regime/genocide to feel connected.
Of course the most obvious solution is to go low contact which I already do. To be fair, it was already difficult in the past as he had a lot of pretty controversial viewpoints- supporting Trump (cos this was good for China?) , supporting Brexit (cos this would allow more non EU immigration). I mean, there are probably a significant percentage of the population who support Trump and Brexit probably for equally spurious reasons so there is no point getting upset about that. But I draw the line at genocide.