Hello,
I was browsing for answers on this forum because I seem to be experiencing similar issues. I've been using Calibre on macos, with no problem including with Catalina until I upgraded to version 5.42. Since then, the icon jumps up and down for a while and nothing happens. I've also tried erasing older files except for the library and reverting to older versions that used to work perfectly, etc. but no version of Calibre will open anymore.
I've tried running terminal, to enter the code mentioned above in the thread, but when terminal opened it read:
Spoiler:
Last login: Tue Nov 10 22:33:49 on ttys001
The default interactive shell is now zsh.
To update your account to use zsh, please run `chsh -s /bin/zsh`.
For more details, please visit
https://support.apple.com/kb/HT208050.
and the command /Applications/calibre.app/Contents/MacOS/calibre does not work.
My computer capacity is very limited and I have no idea what to do! Any help would be greatly appreciated. Many thanks in advance.