Python Plugins for QGIS: where to put own packages

I wrote some special packages for a specific problem inside our company. For a better handling I decided to integrate it into QGIS as a plugin.

I followed the instructions of the tutorial Building a Python Plugin (QGIS3)

At the end I had a complete and working plugin with a dialog window, but without any functionality. The plugin- code is in AppData\Roaming\QGIS\QGIS3\profiles\default\python\plugins, as the other plugins.

I tried to put a subfolder "dummy" inside ...plugins\my_project, including __init__.py But it was impossible to use any function declared in dummy.

Where do I have to put my packages, so that I can use it? There is no mix between Qt and my code, strictly top- down.

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