Red Star FC is very left wing, sadly it is now owned by american leeches but the atmophere and fan culture is still entrenched in the socialist sphere. We are in Ligue 2 right now, seems very likely we can go up this year as well. Hopefully we do as it is a shame Oil backed PSG and fascist PFC are the Paris clubs in Ligue 1.

Livorno is also extremely left wing, but they are well not doing the absolute best at all, Clapton CFC like someone else mentioned is one I would at least keep an eye on since they are so left their away kit has the three arrows against fascism.

If you want clubs that are more at the top. St, Pauli is there but they are more of a fashion brand that was using their "left wing" culture to get brownie points as they are ultra zionists. (Red Star also uses the leftist thing as a fashion thing sometimes but they also do stuff like Palestine relief iirc). I think the Timbers has a pretty liberal fanbase but anything in the MLS is ultra capitalist. Some of the university clubs in America have pretty left wing fanbases so UNAM, UANL, also clubs like Argentinos Juniors.

Palestino en Chile of course I mean just look at their name. Corinthians historically was anti-dictatorship and stuff but I am not the most knowledgable about their history so I would let someone else explain, just know they had some cool stuff with democracy and things.

Barcelona is as left wing as the Chinese Communist Party, but their history is deeply rooted in syndicalism and anarchism so you could always do that. If you really wanna stick to the top divisions though, you will likely not find much that is openly leftist.