Originally posted by @eddyizm in #1873

@freakboy3742 Yeah, sorry I should have added more context.
I am currently working on a small port and have a working toga environment using briefcase in a virtual environment. I am making progress and stumbled across toga-demo so figured i'd give it a go in the same repo.

pip install toga-demo

Installing collected packages: toga-demo
Successfully installed toga-demo-0.5.0

toga-demo
(replaced my path with $HOME)

Traceback (most recent call last):
  File "$HOME/env/lib64/python3.13/site-packages/toga/icons.py", line 32, in __get__
    value = getattr(cls, f"__{self.f.__name__}")
AttributeError: type object 'Icon' has no attribute '__APP_ICON'. Did you mean: 'APP_ICON'?

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "$HOME/env/lib64/python3.13/site-packages/toga_gtk/icons.py", line 36, in __init__
    native = GdkPixbuf.Pixbuf.new_from_file(str(path)).scale_simple(
             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
gi.repository.GLib.GError: gdk-pixbuf-error-quark: Couldn’t recognize the image file format for file “$HOME/env/lib64/python3.13/site-packages/toga_demo/resources/toga-demo.ico” (3)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "$HOME/env/bin/toga-demo", line 8, in <module>
    sys.exit(run())
             ~~~^^
  File "$HOME/env/lib64/python3.13/site-packages/toga_demo/__main__.py", line 6, in run
    main().main_loop()
    ~~~~^^
  File "$HOME/env/lib64/python3.13/site-packages/toga_demo/app.py", line 106, in main
    return TogaDemo("Toga Demo", "org.beeware.toga-demo")
  File "$HOME/env/lib64/python3.13/site-packages/toga/app.py", line 291, in __init__
    self.icon = Icon.APP_ICON
                ^^^^^^^^^^^^^
  File "$HOME/env/lib64/python3.13/site-packages/toga/icons.py", line 34, in __get__
    value = self.f(owner)
  File "$HOME/env/lib64/python3.13/site-packages/toga/icons.py", line 57, in APP_ICON
    return Icon(_APP_ICON)
  File "$HOME/env/lib64/python3.13/site-packages/toga/icons.py", line 121, in __init__
    self._impl = self.factory.Icon(interface=self, path=full_path)
                 ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "$HOME/env/lib64/python3.13/site-packages/toga_gtk/icons.py", line 45, in __init__
    raise ValueError(f"Unable to load icon from {path}")
ValueError: Unable to load icon from $HOME/env/lib64/python3.13/site-packages/toga_demo/resources/toga-demo.ico

briefcase --version
0.3.22

python --version
Python 3.13.3

 uname -a
Linux fedora 6.14.3-200.fc41.x86_64 #1 SMP PREEMPT_DYNAMIC Mon Apr 21 13:49:26 UTC 2025 x86_64 GNU/L

cat /etc/os-release
NAME="Fedora Linux"
VERSION="41 (KDE Plasma)"
RELEASE_TYPE=stable
ID=fedora
VERSION_ID=41
VERSION_CODENAME=""
PLATFORM_ID="platform:f41"
PRETTY_NAME="Fedora Linux 41 (KDE Plasma)"
ANSI_COLOR="0;38;2;60;110;180"
LOGO=fedora-logo-icon
CPE_NAME="cpe:/o:fedoraproject:fedora:41"
DEFAULT_HOSTNAME="fedora"
HOME_URL="https://fedoraproject.org/"
DOCUMENTATION_URL="https://docs.fedoraproject.org/en-US/fedora/f41/"
SUPPORT_URL="https://ask.fedoraproject.org/"
BUG_REPORT_URL="https://bugzilla.redhat.com/"
REDHAT_BUGZILLA_PRODUCT="Fedora"
REDHAT_BUGZILLA_PRODUCT_VERSION=41
REDHAT_SUPPORT_PRODUCT="Fedora"
REDHAT_SUPPORT_PRODUCT_VERSION=41
SUPPORT_END=2025-12-15
VARIANT="KDE Plasma"
VARIANT_ID=kde