Quick hack Mac app to put up a sheet with multi-line text.

ContentView.swift

import SwiftUI

struct ContentView: View {
  @State private var showSheet: Bool = false
  @State private var name: String = "Default Name"

  var body: some View {
    VStack {
      Text("Hello, World!")
        .frame(maxWidth: .infinity, maxHeight: .infinity)
      Button(action: {
        self.showSheet = true
      }, label: { Text("Alert me!") })
      Spacer()
    }
    .sheet(isPresented: $showSheet, content: { TestSheet(name: self.$name) })
  }

  struct TestSheet: View {
    @Environment(\.presentationMode) var presentationMode
    @Binding var name: String
    @State var localName: String = ""

    var body: some View {
      VStack(alignment: .leading, spacing: 10) {
        Text("Title Text")
          .fontWeight(.bold)
        Text("InfoText needs to be long enough that it should wrap so let's do that now. One would hope that this would be enough text... [END]")
          .font(.caption)
          .multilineTextAlignment(.leading)
        TextField("", text: $localName)
        HStack {
          Button(action: {
            self.presentationMode.wrappedValue.dismiss()
          }, label: {
            Text("Cancel")
          })
          Spacer()
          Button(action: {
            self.name = self.localName
            self.presentationMode.wrappedValue.dismiss()
          }, label: {
            Text("Save")
          })
          .frame(alignment: .trailing)
        }
      }
      .frame(width: 400)
      .padding()
      .onAppear {
        self.localName = self.name
      }
    }
  }
}

struct ContentView_Previews: PreviewProvider {
  static var previews: some View {
    ContentView()
  }
}

Turns out it's the line 48 that makes it work.
Others are using .fixedSize(horizontal: false, vertical: true) to make theirs work but that makes the sheet sizing go crazy for me. ¯_(ツ)_/¯