When trying to start the current version of  Calibre (6.1.0) from command line
it aborts:

> calibre
Traceback (most recent call last):
  File "/usr/bin/calibre", line 21, in <module>
    sys.exit(calibre())
  File "/usr/lib64/calibre/calibre/gui_launch.py", line 72, in calibre
    main(args)
  File "/usr/lib64/calibre/calibre/gui2/main.py", line 548, in main
    run_main(app, opts, args, gui_debug, si, retry_communicate=True)
  File "/usr/lib64/calibre/calibre/gui2/main.py", line 560, in run_main
    return run_gui(opts, args, app, gui_debug=gui_debug)
  File "/usr/lib64/calibre/calibre/gui2/main.py", line 403, in run_gui
    run_gui_(opts, args, app, gui_debug)
  File "/usr/lib64/calibre/calibre/gui2/main.py", line 413, in run_gui_
    from calibre.gui2.ui import Main
  File "/usr/lib64/calibre/calibre/gui2/ui.py", line 41, in <module>
    from calibre.gui2.ebook_download import EbookDownloadMixin
  File "/usr/lib64/calibre/calibre/gui2/ebook_download.py", line 8, in <module>
    from mechanize import MozillaCookieJar
ModuleNotFoundError: No module named 'mechanize'

As I don't run Calibre very often I don't know if it is a problem with Calibre
version or "mechanize" which was updated from 0.4.7 to 0.4.8 yesterday
(python38-mechanize/python310-mechanize).