To install external Python module to the package provided with Agisoft Metashape Professional it is necessary to perform the following single-line command from the command-line / terminal depending on the OS used and the name of the Python module to be installed:

on Windows (run cmd.exe with the administrator privileges):

"%programfiles%\Agisoft\Metashape Pro\python\python.exe" -m pip install python_module_name

on macOS, starting from version 10.15 Catalina (via Terminal):

/ -m pip install python_module_name

on Linux (via Terminal):

./metashape-pro/python/bin/python3.8 -m pip install python_module_name

In case Linux installation doesn't work due to any reason (like ImportError: cannot import name 'HTTPSHandler') please install libssl 0.9.8 (as shown below) and repeat pip install process:

sudo dpkg -i libssl0.9.8_0.9.8o-7_amd64.deb