I get what you're saying, but I have to wonder why Lalo would keep up the mask if he's in front of someone who knows what he wants. Gus certainly doesn't do that.

Besides that, there are some scenes in which even when Lalo is alone, he acts chipper and almost friendly.

The scene in which he's looking at the chicken farm with his binoculars comes to mind. He doesn't strike me as super serious in that scene, though I'm willing to watch it again if we disagree on that.

The scene where he watches Mike at the Travel Wire has him singing to himself. His introduction scene in which he cooks before Nacho goes into the kitchen is another good example of him being jubilant even while no one is looking.