"Squatter" is a noun. A "squatter" is someone who squats. "To squat" is a verb. It's what a squatter does. To paraphrase Taylor Swift, "squatters gonna squat."

A squatter generally means someone who is living in a house they have occupied illegally. “To squat” is the verb for that but also means to lower your body with your legs under you.

One is a noun and one is a verb.