PyCharm makes possible to use the virtualenv tool to create a project-specific isolated virtual environment. The main purpose of such virtual environments is to manage settings and dependencies of a particular project regardless of other Python projects. virtualenv tool comes bundled with PyCharm, so the user doesn't need to install it.
Create virtual environment with Python 3.5, 3.6, 3.7 or 3.8, install Metashape wheel there (latest version is available from Downloads page) and use interpreter from this python environment in PyCharm:
pip install ~/Downloads/Metashape-1.7.1-cp35.cp36.cp37.cp38-abi3-linux_x86_64.whl
Then go to PyCharm -> File -> Settings... -> Project -> Project Interpreter -> Click -> Add... -> Existing environment -> .../myenv/bin/python
And use "import Metashape.Metashape as Metashape" instead of "import Metashape" in the script body.
With this the auto-completion of Metashape module related commands would work.