SwiftUI for macOS expert to fix

This is a SwiftUI project for macOS only. The objective is to fix the following 5 issues:
It requires an expert for macOS and SwiftUI.

// PROBLEMS to fix:
// 1) the fle name is on the ListView (right side), but not on the dcoument window
// weird: one the list disappears (resize), the window title is correct?
// 2) resizing the document window results in a window without content
// cannot resize horizontally, only resize vertical?
// 3) captions array shoud be declared in SubtitleDocument (not public!)
// if I do that it creates all kinds of errors
// 4) I cannot create some space 7 pixels; below the input fields
// 5) from the SubtitleDocument, how to access selection and input on SubtitleListView
@State private var mySelection: Caption? = nil
@State private var startHours: Int = 0
@State private var startMinutes: Int = 0
@State private var startSeconds: Int = 0
@State private var startMilliseconds: Int = 0