It's a useful shorthand, not a slur

I would argue that demeaning shorthand expressions used in a negative connotation against people who have been systematically discriminated, imprisoned or even assassinated, is an appropriate descriptor of a slur. Communism has been seriously repressed, from "milder" forms like McCarthyism in the US purging communists from all public life and condemning them to unemployment, to more direct methods such as literal extermination through forced labor and murder as in my homeland of Spain. All Marxists from Spain were either murdered or had to emigrate to Mexico or the USSR during the 1930s.

Again, you can admire their public transport without supporting the government

Exactly my point, and the reason for my original comment.

According to it, they've transitioned from putting uyghur in camps to putting them in prisons

Not really. They're documenting the existence of prisons in Xinjiang, but there's absolutely no evidence of mass imprisonment of Uyghurs based on their ethnicity or religion or any other grounds. Prisons exist in all countries, not exclusively in China, and China doesn't have particularly high rates of imprisonment compared to countries like the US.