def concat_generators(*args):
      for gen in args:
          yield from gen
  params = concat_generators(model.img_encoder.fc.parameters(), model.qu_encoder.parameters() , model.fc1.parameters(),  model.fc2.parameters())

  optimizer = torch.optim.Adam(params, lr=learning_rate)

This may work.
You got an error because you parameters() are not lists, but generators, and you can’t sum generators.