First of all, I saw this question and all the others with similar answer and it does not seem to work for me. I use Ubuntu 19.04 and GNOME 3.32.1
I downloaded Postman (a code testing tool) and I want to be able to launch it from the dock. When I launch it from the shortcut, it appears in the dock:
But when I right-click it, I cannot add it to my favorites, which usually allows me to pin an application to the dock:

I also tried to add a desktop file to /usr/share/applications and ~/.local/share/applications and make it executable, and then restarting gnome, but it did nothing. Desktop file :
[Desktop Entry]
Type=Application
Encoding=UTF-8
Name=Postman
Icon=/home/[my user name]/Utilities/Postman/app/resources/assets/icon.png
Exec=/home/[my user name]/Utilities/Postman/app/Postman
Terminal=false
Categories=Development;

.Desktopfile executable. Did you try little tool calledalacarteto create a launcher ? – pLumo Aug 20 '19 at 14:47.desktopfile. – Tom Aug 20 '19 at 14:48