Unable to build repo on Mac OS X 10.15.7 with Xcode 12.4

[Scott M Stark]

I just cloned the flutter-folio repo and ran through the build instructions

✏️ [starksm@Scotts-iMacPro#1115]-(flutter-folio)-[git://master ✔]-
└> flutter upgrade
Flutter is already up to date on channel stable
Flutter 2.2.0 • channel stable • https://github.com/flutter/flutter.git
Framework • revision b22742018b (13 days ago) • 2021-05-14 19:12:57 -0700
Engine • revision a9d88a4d18
Tools • Dart 2.13.0└> flutter upgrade
Flutter is already up to date on channel stable
Flutter 2.2.0 • channel stable • https://github.com/flutter/flutter.git
Framework • revision b22742018b (13 days ago) • 2021-05-14 19:12:57 -0700
Engine • revision a9d88a4d18
Tools • Dart 2.13.0
✏️ [starksm@Scotts-iMacPro#1115]-(flutter-folio)-[git://master ✔]-
└> flutter config --enable-macos-desktop
Setting "enable-macos-desktop" value to "true".

You may need to restart any open editors for them to read new settings.
✏️ [starksm@Scotts-iMacPro#1116]-(flutter-folio)-[git://master ✔]-
└> flutter run -d macos
Launching lib/main.dart on macOS in debug mode...
Running pod install...                                              8.4s
note: Using new build system                                            
note: Building targets in parallel                                      
note: Planning build                                                    
note: Constructing build description                                    
warning: The macOS deployment target 'MACOSX_DEPLOYMENT_TARGET' is set to 10.7, but the range of supported deployment target versions is 10.9 to 11.1.99. (in target 'leveldb-library' from project 'Pods')
error: No signing certificate "Mac Development" found: No "Mac Development" signing certificate matching team ID "S3TL5AY6Y3" with a private key was found. (in target 'Runner' from project 'Runner')
warning: The macOS deployment target 'MACOSX_DEPLOYMENT_TARGET' is set to 10.7, but the range of supported deployment target versions is 10.9 to 11.1.99. (in target 'BoringSSL-GRPC' from project 'Pods')
warning: The macOS deployment target 'MACOSX_DEPLOYMENT_TARGET' is set to 10.6, but the range of supported deployment target versions is 10.9 to 11.1.99. (in target 'FMDB' from project 'Pods')
** BUILD FAILED **                                                      
                                                                        
Building macOS application...                                           
Exception: Build process failed
✏️ [starksm@Scotts-iMacPro#1117]-(flutter-folio)-[git://master ✗]-
└> flutter doctor
└> flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 2.2.0, on Mac OS X 10.15.7 19H1030 darwin-x64,
    locale en-US)
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
[✓] Xcode - develop for iOS and macOS
[✓] Chrome - develop for the web
[✓] Android Studio (version 4.2)
[!] Android Studio
    ✗ Android Studio not found at /Users/starksm/Library/Application
      Support/Google/AndroidStudio4.1/Contents
[✓] VS Code (version 1.53.0)
[✓] Connected device (3 available)

! Doctor found issues in 1 category.

I am able to create a shell flutter app and run it as a macOS app without any problems:

✏️ [starksm@Scotts-iMacPro#1133]-(Flutter)
└> flutter create myapp
Recreating project myapp...
  myapp/android/app/src/main/res/values-night/styles.xml (created)
  myapp/android/app/src/main/res/drawable-v21/launch_background.xml (created)
Running "flutter pub get" in myapp...                            1,204ms
Wrote 5 files.

All done!
In order to run your application, type:

  $ cd myapp
  $ flutter run

Your application code is in myapp/lib/main.dart.

✏️ [starksm@Scotts-iMacPro#1134]-(Flutter)
└> cd myapp 
✏️ [starksm@Scotts-iMacPro#1135]-(myapp)
└> flutter run -d macos
Launching lib/main.dart on macOS in debug mode...
Upgrading project.pbxproj
Building macOS application...                                           
Syncing files to device macOS...                                    58ms

Flutter run key commands.
r Hot reload. 🔥🔥🔥
R Hot restart.
h Repeat this help message.
d Detach (terminate "flutter run" but leave application running).
c Clear the screen
q Quit (terminate the application on the device).

Running with unsound null safety
For more information see https://dart.dev/null-safety/unsound-null-safety

An Observatory debugger and profiler on macOS is available at:
http://127.0.0.1:60904/p7YU83KTA7g=/
Activating Dart DevTools...                                      1,769ms
The Flutter DevTools debugger and profiler on macOS is available at:
http://127.0.0.1:9101?uri=http%3A%2F%2F127.0.0.1%3A60904%2Fp7YU83KTA7g%3D%2F
Lost connection to device.