You need to make sure that you have installed the platform plugins when you try to deploy your application. Depending on that you need to deploy things, there are mainly two methods to tell your application the location where the platform plugins are at runtime which should work for you.
To export the path to the directory through the QT_QPA_PLATFORM_PLUGIN_PATH variable.
e.g QT_QPA_PLATFORM_PLUGIN_PATH=path/to/plugins ./my_qt_app
The other option, which is to create a qt.conf file in the same directory which contains your executable. The contents of which would be: