KVO_firstApproach.swift

[...]

// Add observer in layoutSubviews()

pictureImageView.observe(\UIImageView.frame, options: [.new]) { [weak self] (_, _) in
    self?.updateTextViewFrame()
}

[...]

private func updateTextViewFrame() {
    contentView.layoutIfNeeded()
        
    let rect = pictureImageView.convert(pictureImageView.bounds, to: descriptionTextView)
    let imagePath = UIBezierPath(rect: rect)
    descriptionTextView.textContainer.exclusionPaths = [imagePath]
}