Need Help: Launcher or Desktop File not working for a "portable" Application

I installed the cross-platfrom application FreeFileSync on Ubuntu 18.04.
It’s a kind of “portable” application, just unpack it.
I decided to put it to /opt/FreeFileSync, because there are three user on the laptop.
FreeFileSync wites a kind of INI-File to store its settings in the programm directory, so I make /opt/FreeFileSync rwx for all users.

If I start the program with nautilus, everything is nice, but …
I want to add a launcher and the program comes with a .desktop file.

I adapted the pathes in the .desktop file and for test I copy it to my
desktop and start it:
it asks if I trust it, the ICON changed to the FreeFileSync-Icon
and I get “there is an error during start of application”
(not exactly the message, I’m using german localisation)

The error message should nominated for the “Billy Gates Memorial” Price, by-the-way.

Here’s the content of the File FreeFileSync.desktop
[Desktop Entry]
GenericName=Folder Comparison and Synchronization
Exec=/opt/FreeFileSync %f

It seems very simple, but I didn’t find an error, it should work.
I tried a couple of different exec lines like:
Exec=/opt/FreeFileSync %F
and so on

So what I’m doing wrong ???

This is a generic issue that would be readily applicable to all Ubuntu flavours. So and are very useful places you can ask as well.

Suggest also investigate changing the Exec= line to something like Exec=sh -c 'cd /opt/; . ./FreeFileSync' or maybe wrapping the call into a bash script you can then execute with.

Found the error: it’s the line : Categories=System;
with the “;” at the end. Remove and it was fine