Microsoft Planner Connector: Update Task Buckets
It's currently possible to set the bucket ID when creating new Planner tasks, but it's not possible to change a task's bucket in the "Update a Task" action. Please add this feature.
For anyone who ends up here looking for a way to do this, you can edit the code on an Update Task block to include the bucket id. Once you do this, flicking back to the designer will show that parameter on the card and you can use variables etc.