Khmer Rouge was backed by the US and was lead by fascists who rejected Marx, like the Nazis.
I think that’s a highly misleading and highly reductionist interpretation. The Khmer Rouge was supported by the US, but mostly after the conflict had ended.
The Khmer Rouge was overwhelmingly supported by the CCP, especially during the Vietnam war, and before the Chinese invasion of Vietnam afterwards.
Also, PolPot wasn’t criticized for his diversion from Marxism until the 80’s, well after the most turbulent times in Cambodia. And even then Deng Xiaoping only criticised the Khmer Rouge for engaging in “deviations from Marxism-Leninism”
The only person on the left who accused him of being a fascist was Hoxha, but that was after his schism with the maoist. So to him any communist Asian was basically a barbaric fascist.