IOS stackview addArrangedSubview add at specific index

You mean you want to insert, not add:

func insertArrangedSubview(_ view: UIView, atIndex stackIndex: Int)

if you don't want to struggle with the index you can use this extension

extension UIStackView {
    func insertArrangedSubview(_ view: UIView, belowArrangedSubview subview: UIView) {
        arrangedSubviews.enumerated().forEach {
            if $0.1 == subview {
                insertArrangedSubview(view, at: $0.0 + 1)
            }
        }
    }
    
    func insertArrangedSubview(_ view: UIView, aboveArrangedSubview subview: UIView) {
        arrangedSubviews.enumerated().forEach {
            if $0.1 == subview {
                insertArrangedSubview(view, at: $0.0)
            }
        }
    }
}