Is Google Drive File Stream what you have installed? It's my understanding that you have to disconnect the account from file sync in order to quit the program. (see steps below) I do not know of an easy way to just sign out of the file sync. Hopefully, someone else has a better solution.
On your menu bar, click Google Drive icon, then select Preferences .
Click the cog icon the select "Disconnect account." In the pop-up window, click OK.
On the Google Drive website, click your profile icon in the top right corner and select "Sign out."
I hope this helps.