Google Tasks on Google Space in Google Workspace allow to assign user to any task, displayed on Room.
How to get from Google Tasks API assigned user to task? Response hasn't information about this: https://developers.google.com/tasks/reference/rest/v1/tasks#Task
If you create Google Tasks through Google Chat these tasks will only be visible through the Google Task client, these tasks and all their details like assigned user can't be retrieved by the API yet. There is already a feature request but there is no estimate yet on when it will be implemented, you can track updates through here.
