Probably too late to the party but building on top of @Dakai Ou answer I achieved the following effect, using @miblanchard/react-native-slider and the react-native-linear-gradient:

<LinearGradient
  colors={["#e2e8f0", "#f1f5f9", "#fbbf24"]}
  start={{ x: 0, y: 0 }}
  end={{ x: 1, y: 0 }}
  style={[
    styles.linearGradient,
    {
      position: "absolute",
      left: 0,
      right: 0,
      top: "50%",
      transform: [{ translateY: -5 }],
    },
  ]}
/>
<Slider
  minimumTrackTintColor={"transparent"}
  maximumTrackTintColor={"transparent"}
  thumbStyle={{
    backgroundColor: "white",
    width: 24,
    height: 24,
    borderColor: "black",
    borderWidth: 1,
    borderRadius: 12,
    position: "absolute",
    top: "50%",
    marginTop: -12,
  }}
/>