Hi @Anonymous,
Could you share a screenshot of your Flow configuration?
If you want to the task assigned to you is synced to Todoist, you could use "When a task is assigned to me" as the trigger.
This will only trigger Flow when the task assigned to you is created, and create and display the task assigned to you in Todoist.

If you want to synchronize the existing Planner task assigned to you to Todoist, you could configure "List my tasks" action, which will list all the tasks assigned to you.
Then you could configure Todoist with the output of this action.

Best Regards,
Barry