Oi Deborah,

Posta aqui o código da sua interface TopicoRepository.

package br.com.alura.forum2021.repository;

import org.springframework.data.jpa.repository.JpaRepository;

import br.com.alura.forum.modelo.Topico;

public interface TopicoRepository extends JpaRepository<Topico, Long> {

}

package br.com.alura.forum2021.controller;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController;

import br.com.alura.forum.modelo.Topico; import br.com.alura.forum2021.controller.dto.TopicoDto; import br.com.alura.forum2021.repository.TopicoRepository;

@RestController public class TopicosController {

@Autowired
private TopicoRepository topicoRepository;


@RequestMapping("/topicos")
public List<TopicoDto>  lista() {

    List<Topico> topicos = topicoRepository.findAll();
    return TopicoDto.converter(topicos);


}

}

Eu tinha criado o pacote forum. modelo e era para colocar foram2021.modelo, agora foi. Obga!