Where and how can I run the ebook-convert script for calibre from the console?
nicholas@gondor:~$ 
nicholas@gondor:~$ flatpak info com.calibre_ebook.calibre
calibre - The one stop solution to all your e-book needs
      ID: com.calibre_ebook.calibre
     Ref: app/com.calibre_ebook.calibre/x86_64/stable
    Arch: x86_64
  Branch: stable
 Version: 5.23.0
 License: GPL-3.0
  Origin: flathub
Collection: org.flathub.Stable
Installation: system
   Installed: 360.9 MB
     Runtime: org.freedesktop.Platform/x86_64/20.08
         Sdk: org.freedesktop.Sdk/x86_64/20.08
  Commit: 13464e660f35716a725261af4b45d3abc199a3ce52ebdd9ee887c7ae623b5873
  Parent: 4f7f3b603f31cc781caf8260f887118a1bb466748891c9e122826728e25d3eed
 Subject: Update calibre-5.22.1-x86_64.txz to 5.23.0 (9184a3f3)
    Date: 2021-07-11 19:56:21 +0000
nicholas@gondor:~$ 
nicholas@gondor:~$ uname -a
Linux gondor 5.8.0-59-generic #66-Ubuntu SMP Thu Jun 17 00:46:01 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
nicholas@gondor:~$ 
nicholas@gondor:~$ man calibre
No manual entry for calibre
nicholas@gondor:~$ 
nicholas@gondor:~$ ebook-convert
Command 'ebook-convert' not found, but can be installed with:
sudo apt install calibre
nicholas@gondor:~$ 
Installed via flatpak because:
1.)  calibre is, or at least wasn't, in snap repo
2.)  have had problems with the apt version in the past
more of a flatpak usage q than specific to Ubuntu.  Probably a calibre or flatpak man page will explain where or how to launch the conversion script -- but which man page?
tried:
nicholas@gondor:~$ 
nicholas@gondor:~$ flatpak run com.calibre_ebook.calibre.ebook-convert
error: app/com.calibre_ebook.calibre.ebook-convert/x86_64/master not installed
nicholas@gondor:~$ 
nicholas@gondor:~$ flatpak run com.calibre_ebook.ebook-convert
error: app/com.calibre_ebook.ebook-convert/x86_64/master not installed
nicholas@gondor:~$ 
see also