Sample to show a blog writer a way to do what they wanted (lined up field values) that actually worked. Put this in an iOS app project and you can preview just this view and if you edit the text in the fields you can see it all adjust. Comment in the .border(Color.green) lines to see the frames of the Text views change dynamically as you type :)

SampleView.swift

//
//  ContentView.swift
//  bugtest
//
//  Copyright © 2020 Geek & Dad, LLC All rights reserved.
//

import SwiftUI

struct PreferenceTest: View {
  @State var value1 = ""
  @State var value2 = ""
  @State var value3 = ""
  @State var width: CGFloat? = nil
  let labelToFieldPadding: CGFloat = 20.0
  
  var body: some View {
    Form {
      HStack {
        Text("1")
          .frame(width: width, alignment: .leading)
          .background(ColumnWidthEqualiserView())
          // .border(Color.green)
        TextField("Enter first item", text: $value1)
          .textFieldStyle(RoundedBorderTextFieldStyle())
          .padding([.leading], labelToFieldPadding)
      }
      HStack {
        Text("123456")
          .frame(width: width, alignment: .leading)
          .background(ColumnWidthEqualiserView())
          // .border(Color.green)
        TextField("Enter second item", text: $value2)
          .padding([.leading], labelToFieldPadding)
          .textFieldStyle(RoundedBorderTextFieldStyle())
      }
      HStack {
        Text("123")
          .frame(width: width, alignment: .leading)
          .background(ColumnWidthEqualiserView())
          // .border(Color.green)
        TextField("Enter third item", text: $value3)
          .padding([.leading], labelToFieldPadding)
          .textFieldStyle(RoundedBorderTextFieldStyle())
      }
    }.modifier(ColumnWidth(width: $width))
  }
}

struct ColumnWidthEqualiserView: View {
  var body: some View {
    GeometryReader { geometry in
      Rectangle()
        .fill(Color.clear)
        .preference(
          key: ColumnWidthPreferenceKey.self,
          value: [ColumnWidthPreference(width: geometry.frame(in: CoordinateSpace.global).width)]
        )
    }
  }
}

struct ColumnWidthPreference: Equatable {
  let width: CGFloat
}

struct ColumnWidthPreferenceKey: PreferenceKey {
  typealias Value = [ColumnWidthPreference]

  static var defaultValue: [ColumnWidthPreference] = []

  static func reduce(value: inout [ColumnWidthPreference], nextValue: () -> [ColumnWidthPreference]) {
    value.append(contentsOf: nextValue())
  }
}

struct ColumnWidth: ViewModifier {
  @Binding var width: CGFloat?
  func body(content: Content) -> some View {
    content
      .onPreferenceChange(ColumnWidthPreferenceKey.self) { preferences in
        // early in initialization we are called with empty array so guard against that case
        guard preferences.count > 0 else { return }

        let newWidth = preferences
          .map { $0.width }
          .reduce(0, CGFloat.maximum)

        // only set width if we actually have a larger value or if it's unset
        if let w = self.width {
          if newWidth > w {
            self.width = newWidth
          }
        } else {
          self.width = newWidth
        }
      }
  }
}

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