I assume you mean the last World Cup in Qatar in 2022 where Brazil lost in the Qatar finals against Croatia. I don't think the Samba Boys performed very poorly because they lost to a good side on penalties. They indeed lost to a lowly-rated team like Cameroon but we shouldn't also forget that the winner of the World Cup Argentina lost to Saudi Arabia. The rumor that the Brazilian national team will hire Carlo Ancelotti has been laid to rest after the Italian tactician extended his contract with Real Madrid.
But with the appointment of Dorival Júnior as new coach the team has hope of getting some positive results. The former Flamengo, Fluminense, and Santos coach has lots of experience and has won prestigious trophies like the Copa Libertadores and the Brazilian Cup. He also helped Vasco da Gama to win the Seria B title. The 61-year-old tactician has lots of experience that can be useful to the Seleção Canarinha.
I believe that the World Cup in Qatar in 2022 had several unforeseen events, Germany was eliminated at the beginning, Morocco finished in 4th place, Japan beat Germany, Brazil lost to Cameroon, Morocco beat Spain... I'm not belittling these teams, I'm just sharing that sometimes unforeseen events happen and the weakest can surprise.
If Ancelotti became coach of the Brazilian national team, that would be a game changer and that would improve the team a lot, but even so, Dorival Jr is an excellent coach, as you already said, I'm looking forward to seeing how Brazil's performance will be with him as technician.