I faced the same problem and found that it seems SKLabelNode’s attributedText correctly recognizes “.SFUI-Regular”. The code below displays the san-serif font.
label.attributedText = NSAttributedString(string: "blah-blah-blah", attributes: [.font: UIFont.preferredFont(forTextStyle: .body)])
Thank you so much for replying! I wonder why it changed in iOS 13.
I'm facing an issue where I'm unable to use the 'Heavy' or 'Bold' system fonts on a SpriteKit SKLabelNode. When I do what you've suggested and use the string "SFUI-Semibold" etc, the displayed font is still just SFUI-Regular.
I have reported this to apple as a bug.