I'd like to elaborate a little more on why "autistic masking" is different from "neurotypicals' masking".

For neurotypicals, masking is to exhibit behaviors that you subconciously know how to do because they are part of your natural range of behaviors. When a neurotypical is masking being friendly and happy in a social occasion (when they actually don't feel like it), they draw on their previous experience of having been friendly and happy in another social occasion. They know what it feels like, they know how to behave instinctively whey they really are happy and friendly, and faking it is only the effort of drawing from prior experience. For actors, this is called "the Method".

For autists, masking is emulating behaviors they wouldn't normally exhibit on any such occasion. They don't know how to do it, not subconciously, not instinctively. So they explicitly have to observe others, emulate their behavior on that occasion. That leads to two kinds of problems: First, they need to have observed this behavior, learned and practiced it, and need to know how to reproduce it correctly. Second, they need to recognize the occasion correctly, and not misinterpret their surroundings, the feelings and moods of others. And since autists also do have problems even interpreting their own emotional state (they do have emotions, but no intuitive way to know what they are at the moment) and even more the emotional state of others, the effort is far higher. Imagine an actor who is asked to play a totally alien role without any frame of reference and without prior experience, no do-overs and all the other people around him are also directors and constantly judging his performance and measuring it against their effortless instinct what it should look like.