Problem
First of all: I am really happy that it seems like I finally found a working Google Drive client for Linux, overGrive. It seems to be written in Python and, unfortunately is not open source, but rather costs $4.99. But that is fine as long as it actually works.
However, I had some issues when trying to install overGrive for the first time. I am using Ubuntu 18.04, so I followed the official installation instructions, including downloaing the .deb package and installing it with dpkg. I could see overGrive in Gnome’s app launcher afterwards, but when I clicked it, nothing happened. It did not start without any error message.
Solution
The solution was the following. I figured out that overGrive is by default installed to /opt/thefanclub/overgrive and the binary can be run with Python (2.7), like python /opt/thefanclub/overgrive/overgrive. This gave me the error message that No module named oauth2client.client. After googling I found that I manually had to install these Python modules in addition.
sudo pip install google-api-python-clientsudo pip install oauth2client
If pip complains about further missing dependencies while installing one of the above packages, simply pip install them, too.
Good luck! And again, thanks to thefanclub for this Google Drive sync client.
EDIT: After a few days I found that OverGrive did not work well at all, unfortunately. Syncs produced inconsistent states and the client “logged out” randomly after rebooting. Eventually, I set up a NextCloud and migrated from Google Drive. I was already pleased with NextCloud a few months ago and only switched to GDrive because of Google Docs, but that’s not worth the cr****y clients (the official Windows client is not quite better). NextCloud has a great web interface, sync clients for all major platform, a decent Android app and is open-source :-)