Frankly, un-masking has been one of the main topics of my therapy since over a year. It's not so easy to drop habits that one has been using for all their life. I believe there is no easy solution. I still unconsiously get back to it every now and then.
Unmasking included learning to give myself space to quarrel with people. That was super hard, I'm scared of quarrelling because in my childhood it always triggered meltdowns that left me vulnerable and exposed. My therapist was adamant about finding my anger while I was believing I was simply incapable of expiriencing this emotion... after a year of trying my inlaws p*ssed me off to the point I released over 20 years of swallowed anger on them. They didn't take it well... but after a few months even my relationship with them is better than it used to be.
I don't know of any book or technique. It's just slow, tedious process of learning to identify my own needs and emotions, validating them and letting myself act on them. Learning new social skills that allow me to do it next to other people. Including quarrels.
I'm sure my parents are very uncomfortable with me unlearning all the "good behavior" they put so much effort into teaching me. I admit I feel some trolling satisfaction about it.
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Let's not confuse being normal with being mentally healthy.
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