Office 365 (Outlook 2013 / 2016 / 2019 for Win) - Share Your Tasks Folder
When used with a Microsoft Exchange account, tasks can be shared between people. Task sharing is not limited to just the default Tasks folder that is created in all Outlook profiles. You can create additional task folders and choose which of those folders to share. For example, you can create a task folder for a specific project. You can then share access to the task folder with your co-workers so that they can review the task list.
Tip: Any message, contact, or task in Outlook can by marked private so that others will not see the item when sharing folders.
Task sharing works through sharing invitation and sharing request e-mail messages. Sharing invitations offer the recipient access to your task folder.