Recognise the extra credential you created
An ordinary sign-in and creating a passkey are different events. Google recommends creating passkeys only on devices you personally own and use. Its warning matters on a family computer, borrowed laptop or support machine: someone able to unlock that device can potentially use the stored credential after the current browser session ends. Closing the tab is not the relevant cleanup.
Review the intended account and credential
On a device you can safely access, open your Google Account’s Security and sign-in area, then Passkeys and security keys. Google’s instructions let you select and remove a passkey you created. Check which Google account is selected if several are signed in. Automatically generated Android passkeys have a documented device-sign-out route instead, so do not treat every entry as an identical manually created credential.
A remaining suggestion can come from the credential manager
Google notes that a removed account passkey can still be suggested by a third-party credential manager; its stored copy may need separate removal using that manager’s own guidance. That does not justify deleting every saved login in the browser. Record which unwanted credential you removed and retain a working recovery method. For a borrowed computer used to solve a viewing-account problem, keep the Google credential cleanup separate from the viewing service’s own sign-out and account settings.
Questions, answered
Is closing the browser enough to remove the new passkey?
No. Review and remove the unintended passkey through the documented account and credential-manager controls.