@Christian-Ehrlicher @SGaist I think I managed to solve the problem. The problem is that the webp library is not included in the Qt installation directory. I mean, by default, in the path /Users/user/Qt/6.4.2/macos/plugins/imageformats, only the following libraries are included in my case:
I understand that for this reason, when macdeployqt generates the final application directory, it does not include the webp library.
However, I have been able to find much more libraries in the path /Users/user/Qt/QtDesignStudio/qt6_design_studio_reduced_version/plugins/imageformats, including the following one:
All I had to do is to copy libqwebp.dylib
to /Users/user/Qt/6.4.2/macos/plugins/imageformats, build the final project executable again, and it works.
Thanks a lot to both of you! :))