iOS Builds failing with "unsupported option '-mno-thumb' for target..." in Unity 2019, 2020

Learn how to resolve this issue with building for iOS in Unity 2019.x and 2020.x

There an issue with building for iOS in Unity 2019 and 2020 where XCode fails with exception, "unsupported option '-mno-thumb' for target...", such as:

This issue is a Unity->Xcode output bug, described here:  https://discussions.unity.com/t/xcode-16-1-build-failing-unsupported-option-mno-thumb-for-target-arm64-apple-ios11-0/1563505/3 

To fix the issue:

1. Locate the Build Settings:
   1. Open your project in Xcode.
   2. Select your project from the Project Navigator (left-hand side).
   3. Choose the Unity-iPhone target.
2. Search for Other C Flags and Other C++ Flags:
   1. Go to the Build Settings tab.
   2. In the search bar at the top-right, type Other C Flags.
   3. Look for the entries under Custom Compiler Flags as shown below.
      
      
3. Edit the Flags:
   1. Double-click the entry for each configuration (Debug, Release, etc.) where -mno-thumb appears.
   2. A text input box will appear showing the list of flags.
   3. Remove -mno-thumb from the list.
4. Repeat for Other C++ Flags:
   1. Perform the same steps for Other C++ Flags.
5. Save and Rebuild:
   1. Save the changes (it updates automatically in Xcode).
   2. Clean the project (Product > Clean Build Folder or Cmd+Shift+K).
   3. Rebuild the project.