The calendar planner lasted two days on your phone. Its connection to your account may last much longer. Removing an app from a device and withdrawing permission in an online account are separate jobs.
Start with the permission, not the name
Open your Google Account’s third-party connections page from the account settings. Check which account you are using, especially if you have personal and work profiles. Then open the details of a service you no longer recognise or use.
Google distinguishes several connections. “Sign in with Google” provides a way to log in to another service. Access to your Google Account can instead let an app use particular data or features. A link can also work in the opposite direction, allowing Google to access another service. One app may have more than one type of connection.
An entry in the list therefore does not, by itself, mean the app can read your email. Read what was actually granted.
Avoid breaking your only way in
If you still use the service, check how you would sign in after removing the Google login connection. Whether another login method is available depends on that service. Make sure it works before removing your only convenient route to important files.
For an abandoned calendar tool, review the calendar permissions and remove the connection you no longer need. Afterwards, return to the connections list and check its details again; do not stop at uninstalling the phone app.
Previously copied data is a separate question
Revoking access does not recall information the service already received. If you also want an old account or stored copies removed, review that provider’s account and deletion settings separately.
A useful note for your own records is simply the service name, the connection removed and the date. There is no need to keep a screenshot containing your email address or private calendar entries just to remember that the review happened.