I don’t think Han supremacy/replacement theory has a singular origin. I think it comes from a confluence of:

• Chinese state imperialism theory
• Recycling of white supremacist great replacement theory
• Projection of white supremacy itself
• Rolling up Tibet/Uyghur/Hong Kong into one big undifferentiated ball of Han/CPC oppression

In fact quite the opposite has been happening thanks to China's affirmative action policies