Custom UISlider inner bar corner radius issue iOS 14

You can use if let…

override func layoutSubviews() {
    super.layoutSubviews()
    if let arrSubLayer = layer.sublayers, arrSubLayer.count > 1 {
      arrSubLayer[1].cornerRadius = 12
    }
    self.thumbTintColor = .clear
}

It will check for the sub layers. If any then it will check the count > 1 as you are trying to trying to access index 1.