Why does a desktop launcher does not start my app, while command line does?

this is mostly a comment but could become an answer. we really need more information to be able to help you.

please post:

• your "command line" environment (the output of set when using bash),
• the content of the .desktop file of your created launcher (most likely found in ~/Desktop) and
• the exact shell commands leading up to the program start correctly.
• the output of file /opt/the/programm/youre/attempting/to/run
• the content of /opt/the/programm/youre/attempting/to/run IF the output of find does not contain the word "binary". However there may be copyright/licensing issues with that!

A wild attempt at an answer without any of the above information:

Your software installed in /opt/... is not a statically linked binary but requires some libraries which are also installed below /opt but your system does not know to search that directoy for required libraries. One way to fix this is setting the LD_LIBRARY_PATH variable to include your directory in /opt.