Currently, Gravity Forms does not have a built-in range slider (but maybe soon 🤞🏼).
Fortunately, there are a few third party add-ons that make it possible to still use range sliders with Gravity Forms:
#1 Advanced Number Field by GravityWP
What is a Range Slider?
Range sliders allow you to select a numeric value within a specific range, i.e a minimum or maximum value.
It’s a fancy way of selecting a number. And it looks like this: