What is the current Teams vision you are using?
The Planner app should have been renamed to “Tasks by Planner and To Do”.
Please refer to this link: The “Planner” app name in Teams has changed to “Tasks by Planner and To Do”
I wonder if you are using a quite old version.
And if you have feedback on this, please consider posting in the feedback forum.
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Thank you again @Kael Yao-MSFT
I have submitted my feedback to Microsoft feedback form.
February 2021 - the business went Go Live with Teams and Teams Planner.
Planner was either; added to a Teams Channel as a Tab along the top. or Planner was added as an app to the Teams app pane on the left side.
I understand Planner is old and has been replaced by Tasks By Planner To Do.
If Planner is already setup, (all organisation) it remains. it is not replaced by Tasks By Planner To Do.
In Teams, If I add an app, the new Tasks by Planner To Do is available.