I added a Google Drive source but got an authentication/access error when it tried to generate the list of options for drives to watch.
I was able to fix this by going to Accounts and reconnecting my Google Drive account. During the reconnect process it requested scopes to do more things and after that I was able to configure the source with no issues.
A better UX would be to pop up a reconnect prompt when a scope error happens, or at least provide instructions for how to manually go and reconnect the account.
But I am proud of myself that I figured out how to fix it on my own!