Dear Maintainer,

*** Reporter, please consider answering these questions, where appropriate ***

   * What led up to the situation?
$ sudo apt modernize-sources

   * What exactly did you do (or not do) that was effective (or
     ineffective)?
Synaptic, menu Settings, Sources

   * What was the outcome of this action?
No dialog box appear, and Python Stacktrace appear in the console

   * What outcome did you expect instead?
Sources will be reloaded

*** End of the template - remove these template lines ***

here the stack trace:


Traceback (most recent call last):
   File "/usr/bin/software-properties-gtk", line 100, in <module>
     app = SoftwarePropertiesGtk(datadir=options.data_dir,
options=options, file=file)
   File
"/usr/lib/python3/dist-packages/softwareproperties/gtk/SoftwarePropertiesGtk.py",
line 243, in __init__
     self.show_keys()
     ~~~~~~~~~~~~~~^^
   File
"/usr/lib/python3/dist-packages/softwareproperties/gtk/SoftwarePropertiesGtk.py",
line 1078, in show_keys
     for key in self.apt_key.list():
                ~~~~~~~~~~~~~~~~~^^
   File "/usr/lib/python3/dist-packages/softwareproperties/AptAuth.py",
line 59, in list
     process = subprocess.run(cmd, stdout=PIPE, stderr=PIPE, text=True)
   File "/usr/lib/python3.13/subprocess.py", line 554, in run
     with Popen(*popenargs, **kwargs) as process:
          ~~~~~^^^^^^^^^^^^^^^^^^^^^^
   File "/usr/lib/python3.13/subprocess.py", line 1039, in __init__
     self._execute_child(args, executable, preexec_fn, close_fds,
     ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                         pass_fds, cwd, env,
                         ^^^^^^^^^^^^^^^^^^^
     ...<5 lines>...
                         gid, gids, uid, umask,
                         ^^^^^^^^^^^^^^^^^^^^^^
                         start_new_session, process_group)
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   File "/usr/lib/python3.13/subprocess.py", line 1857, in _execute_child
     self._posix_spawn(args, executable, env, restore_signals, close_fds,
     ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                       p2cread, p2cwrite,
                       ^^^^^^^^^^^^^^^^^^
                       c2pread, c2pwrite,
                       ^^^^^^^^^^^^^^^^^^
                       errread, errwrite)
                       ^^^^^^^^^^^^^^^^^^
   File "/usr/lib/python3.13/subprocess.py", line 1801, in _posix_spawn
     self.pid = os.posix_spawn(executable, args, env, **kwargs)
                ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] File o directory non esistente:
'/usr/bin/apt-key'

apparentrly the stack trace is connected with the use of the now
deprecated apt-key, but appear only on:

menu Settings, Sources