Why can't a guest user add a private task - doesn't have permission

I have set up a GUEST user in my intranet in Zoho CONNECT and on logging in as that that user they are unable to add a private task. Zoho has the option greyed out with a message saying "you do not have permission to add private tasks"

I can't find any reference to why this would be or where any such permission is set.

The user can add a task and then assign it to themselves on a Board but not as a private task.

Can anyone explain what I have overlooked or is there some limitation set in Zoho for "guest" users?

Thanking you... Greg

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