It's possible as I tried building such a kind of flow. In fact, it's really cumbersome as there are only 3 triggers available in Planner, namely When a task is assigned to me, When a new task is created, When a task is completed.
First, create a SharePoint list to record tasks' bucket info;
Then use Recurrence flow to List tasks, compare the latest bucketId with the item from SP list;
If it changes, send a message to Teams; and update the SP list as well.