Windows 11 Pro, 23H2, 22631.3880
Tixati 3.29 and 3.31 do nothing when to configure it to shut down the system after all downloads complete.
I guess it's an issue with not having the admin privileges? Auto-Shutdown did work when I had a Windows 10 OS where I was under the Admin account.

I dont use win 11, but cant you run under the admin account for win11?
I would guess that if it cant shutdown you computer it does not have permission, which is not really a tixati problem.
you have to give it permission.

Tixati fails to mention that admin privileges are required for the shut down feature to work. It doesn't even display any error.
Modern apps usually have their own method of auto obtaining privileges when required.