On my Windows 10 PC there are (at least) 2 Python 3.7 versions installed:
a) "Standard Python 3.7 64 bit with IDLE, which I downloaded from the site python.org and installed.
b) The Python 3.7 which comes bundled with the QGIS network-installer OSGeo4W which installed QGIS in the folder c:\OSGeo4W64
I need to install some Python-Packages via pip in the Python-version, which is used by QGIS. I dont want to "mess up" my Standard installation of Python.