代码问题
1-如果要使用updateMany更新一个元素，请使用updateOne
2-尝试在不正确的for循环中发送响应
3-建议：不要使用promises或async/await（promises另一种语法）回调
请尝试以下操作

app.post("/respostaAprovChamado", function (req, res) {
  if (req.isAuthenticated()) {
    const updatePromises = [];
    for (let i = 0; i < req.body.indiceAprov; i++) {
      updatePromises.push(Chamado.updateOne(
        { "_id": req.body.idChamadoPost, ["listaAprovadores." + i + ".nome"]: req.user.realNome },
        {
          $set: { ["listaAprovadores." + i]: [{ nome: req.user.realNome }, { status: req.body.respostaAprov }] }
        },
        {
          returnNewDocument: true
        }))
    };
    Promise.all(updatePromises)
      .then(result => res.redirect('/aprovChamados'))
      .catch(error => res.send(error))
  } else {
    return res.redirect('/login')
  }
})

或使用async/await

app.post("/respostaAprovChamado", async function (req, res) {
  try {
    if (req.isAuthenticated()) {
      const updatePromises = [];
      for (let i = 0; i < req.body.indiceAprov; i++) {
        updatePromises.push(Chamado.updateOne(
          { "_id": req.body.idChamadoPost, ["listaAprovadores." + i + ".nome"]: req.user.realNome },
          {
            $set: { ["listaAprovadores." + i]: [{ nome: req.user.realNome }, { status: req.body.respostaAprov }] }
          },
          {
            returnNewDocument: true
          }))
      };
      await Promise.all(updatePromises)
      return res.redirect('/aprovChamados')
    } else {
      return res.redirect('/login')
    }
  } catch (error) {
    return res.send(error)
  }
})