I think he is a normal leftist/socdem. He left the Communist Party of Brazil (current in coalition with Lula's Workers' Party and Green Party) at Lula's request in 2023 to join the Socialist Party of Brazil (Party of Lula's VP).

The right-wing hates him because he kept trolling them. Some people said Lula also gave him this seat the the Supreme Court for two reasons.

First, as a thanks for his loyalty and service to Brazil (And Lula got to flex his power in the Senate by electing his lawyer and a communist to the supreme court. Lula said it, probably to mock Bolsonaro. Bolsonaro had said previously "we got now a true Christian supreme court judge, in reference to his two judges, who are now isolated in the court").

Second, to keep him away from running in the 2026 Presidential Elections, since was a popular more left-wing "authoritarian" candidate (Lula is still more popular than him, I don't think theres a candidate that can win against Lula). Also, he looks like Peter Griffin, but if Peter was Brazilian and pardo (mixed ethnicity).

During questioning by the Congress, the Minister of Justice, Flavio Dino, is often attacked by members of the far-right, with questions such as his alleged participation in the invasion of the Planalto Palace on January 8, 2023 (Bolsonaro's Coup attempt), his connection to the PCdoB (Communist Party of Brazil) and his alleged links to organized crime. Dino usually responds with catchphrases, which go viral on the internet.

"You don't know how happy I am today. For the first time in the history of this country, we've managed to put a communist minister on the Supreme Court, a comrade of the quality of Flávio Dino," said Lula during the 4th National Youth Conference in Brasília.