Sharing a To Do list with people outside my organisation

Hi Sarah. You have probably figured this out by now, but you cannot share a ToDo list outside your organization in Microsoft 365. However, you can share with multiple users and organizations from ToDo in Outlook.com. Personally I have created a shopping list with my Microsoft 365 user and my wife's outlook.com user. Works great.

If you want to collaborate with external resources you need to have them part of a planner group.

I talked about this in my practical approach to tasks in Teams at TeamsNation. Check it out in this YouTube video at 4:46: https://youtu.be/fJo0fdv4Fmg?t=286