[PeterT]

I took the approach of initially copying that file to my home directory.
cp /usr/share/applications/calibre-gui.desktop ~/test.desktop

I then edited test.desktop and changed
name=calibre to name=Test

and the line
Exec=calibre --detach %U to Exec=env QT_QPA_PLATFORM=xcb calibre --detach %U

Then did
desktop-file-validate test.desktop
to ensure I had no errors.

Finally did
sudo desktop-file-install test.desktop

I now have a new application in the ChromeBook's Linux Application folder called Test which successfully launches calibre.

After that I cleaned up by removing the test application
sudo rm /usr/share/applications/test.desktop

recopying the calibre-gui.desktop file and making the one required change to it
cp /usr/share/applications/calibre-gui.desktop ~/

Exec=calibre --detach %U to exec=env QT_QPA_PLATFORM=xcb calibre --detach %U


and finally reinstalled the desktop file
sudo desktop-file-install calibre-gui.desktop

My limited testing showed no issues, and no need to edit the other calibre desktop files.

I had NO problems selecting a file in the ChromeBook's File manager app and selecting to open it with calibre.