The word you are looking for is "introversion," not "introvertism."
"Introversion" is a term used to describe a personality trait characterized by a preference for solitude, a need for time alone to recharge, and a tendency to focus more on internal thoughts and feelings. Introverts often feel more energized and comfortable in quieter, less stimulating environments.
On the other hand, "extroversion" refers to a personality trait characterized by a preference for social interactions, enjoying external stimuli, and gaining energy from being around others.
Both introversion and extroversion are considered normal and natural variations of personality, and they exist on a spectrum. Many people may exhibit traits of both introversion and extroversion, and this is often referred to as being an ambivert.
So, in summary, "introversion" is the proper term to describe the personality trait, while "introvertism" is not a recognized word in standard English.