Sample code to implement a vertically gorwing NSTextView in SwiftUI

MainView.swift

import AppKit
import SwiftUI

public struct TextView: NSViewRepresentable {
    @Binding
    var text: String
    var font: NSFont?

    public init(
        text: Binding<String>
    ) {
        self._text = text
    }

    public class Coordinator: NSObject, NSTextViewDelegate {
        var parent: TextView

        init(_ parent: TextView) {
            self.parent = parent
        }

        public func textDidChange(_ notification: Notification) {
            guard let textView = notification.object as? NSTextView else {
                return
            }
            parent.text = textView.string
        }
    }

    public func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }

    public func makeNSView(context: Context) -> NSScrollView {
        let nsView = NSTextView.scrollableTextView()
        let textView = nsView.documentView as! NSTextView
        textView.delegate = context.coordinator
        textView.textContainerInset = .init(width: 10.0, height: 10.0)
        nsView.documentView = textView
        return nsView
    }

    public func updateNSView(_ nsView: NSScrollView, context: Context) {
        (nsView.documentView as! NSTextView).string = text
    }

    public func sizeThatFits(_ proposal: ProposedViewSize, nsView: NSScrollView, context: Context) -> CGSize? {
        let textView = nsView.documentView as! NSTextView
        guard let textLayoutManager = textView.textLayoutManager else {
            return nil
        }
        let rect = textLayoutManager.usageBoundsForTextContainer
        print(rect)
        let width = proposal.width ?? 0.0
        let height = rect.height + textView.textContainerInset.height * 2
        return CGSize(width: width, height: height)
    }
}

struct MainView: View {
    @State
    private var text: String = "This is sample text.\nHello, World!"

    var body: some View {
        VStack {
            ScrollView {
                LazyVStack {
                    ForEach(Array(0..<100), id: \.self) { id in
                        Text("\(id)")
                    }
                }
            }
            .border(.blue)

            TextView(text: $text)
                .border(.red)
                .fixedSize(horizontal: false, vertical: true)
        }
        .scenePadding()
    }
}

#Preview {
    MainView()
}