Bubble's Google Plugin does not allow for users to signup or login to their application through a popup. This is because Google's OAuth experience makes it necessary to navigate to Google's own page for authentication.
For the least disruption to the user's onboarding flow, any Google OAuth workflows/actions can be put at the beginning of user onboarding, so users are able to choose between signing up with traditional workflows, or signing up with Google. This way, users can choose to 'Continue with Google' before entering any signup information.