Hi there all @bdb5424 @Anonymous, there isn't really a need for power automate here. Power Apps can access the planner connector directly and you can therefore create a task straight from the App.
I have just inserted a task direct from a new item as follows:


In order to do this, edit the Power App from within Teams (Power Apps app). Search for and add the planner connector:

Navigate to the create button of the new work item screen and add a call to planner.creattaskv4 as follows:

Here is a very basic example expression:
Planner.CreateTaskV4("d53b0c54-44cb-47c0-aec2-adc7a9f81758","i3wrx3DH-02sFBH13CJnGZcAHLpa",txtAddWorkItemName.Text,{startDateTime:Today(), dueDateTime:datAddWorkItemTargetDate.Value,assignments:"damien@abdndamodev.onmicrosoft.com"});
Note that the planner group id and plan id can be eaily retrieved from the url of the planner online:

Please let me know how you get on - looks like a fun addition.
Please consider accepting my answer as a solution if it helps to solve your problem.
Cheers
Damien
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