Comment 7 for bug 1958120

Oh, /var/log/installer/dm has useful information:

biquity-dm: Traceback (most recent call last):
  File "/usr/bin/ubiquity-dm", line 893, in main
    ret = run(vt, display, username)
  File "/usr/bin/ubiquity-dm", line 868, in run
    ret = dm.run(*sys.argv[4:])
  File "/usr/bin/ubiquity-dm", line 730, in run
    breeze = subprocess.Popen(
  File "/usr/lib/python3.9/subprocess.py", line 951, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/usr/lib/python3.9/subprocess.py", line 1821, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: '/usr/lib/x86_64-linux-gnu//kconf_update_bin/kde4breeze'

(II) Server terminated successfully (0). Closing log file.
Failed to load /usr/share/wallpapers/Next/contents/images/2560x1600.png