yeah but bolsanaro's government is running the election. hard to claim fraud in that case. it will mostly happen when he wins reelection.

The poll was conducted by Ipsos. 538 rates Ipsos a B- for its US election polling. I imagine this poll wasn't perfect but was run by professionals who knew what they were doing.

I can't find an English language page for the poll but here's a Portuguese one: https://www.poder360.com.br/eleicoes/lula-venceria-bolsonaro-no-2o-turno-por-58-a-25-diz-pesquisa-ipsos/

Even US lib media is reporting on this poll, indicating it's at least credible: https://www.bloomberg.com/news/articles/2021-07-05/bolsonaro-s-popularity-hits-lowest-point-amid-vaccine-scandal