@martzj The logic of your flow needs to be adjusted. Take a look at what the Apply to Each action is looping through.

It's looping through each item returned from the List tasks action.
The Update a task action is nested inside the Apply to Each action. This means each time the Apply to Each action loops through (each task) it'll update a task. In your case, it's updating each task in your Planner.
Are you storing the Planner ID in your SP list? If so, you will need to use that dynamic content in the Update a task action. The Apply to Each and List Tasks actions are not required.

Take a look a this YT Tutorial I recently uploaded: 3 Mistakes YOU 🫵 are Making with the Apply to Each Action in your Microsoft Power Automate Flow
In this video tutorial I’ll go over how to avoid these common mistakes when using the Apply to Each action in a Power Automate flow:
1️⃣ Looping through a Single Item
2️⃣ Creating Unnecessary Nested Loops
3️⃣ Looping through an Unfiltered Array
At the end of the video I share a few helpful insights when it comes to using the Apply to Each action in your flow.
I'll also cover:
✅ How to avoid the Apply to Each action with a single item array
✅ How to use the item() function to access dynamic content in an array
✅ How to prevent unnecessary nested Apply to Each action loops
✅ How to use the Select action
✅ How to convert an array to a string with the Select action
✅How to use the Filter Query field
✅ How to count the number of items in an array
✅ How to use a condition control
✅ How to use the concurrency control
✅ How to set a top count
✅ How to use Compose actions for troubleshooting
Hope this helps!