How to save files to Google Drive in Finder?
The Google Drive is located at the root level on your mac. You could just use Spotlight to open the Google Drive folder and move or copy files directly to it. Or just go up levels in the Finder until you get to the root directory.

In my Finder sidebar window, under Devices, I have Macintosh HD as one of the devices. Clicking on this takes tou directly to the root directory. There you should see Google Drive.

Or you can use "Save As" and go up several levels until you see your Google Drive folder and save your file there.