Dermatologist told me dysplastic moles do not turn cancerous and only high dysplasia ones should be removed in case pathologist undiagnosed? Is true?

Basically. If your dermatologist is confident that a particular nevus is dysplastic and not melanoma, leave it on. Keep an eye on your skin. Folks with dysplastic nevi are at greater risk for melanomas. Stay vigilant and you'll be okay.