FreeRTOS will always run the highest priority task that is able to run. When a task is blocked waiting for a notification it is not able to run, when it receives the notification it is waiting for it is able to run.
If the priority of the task giving the notification is higher than the priority of the task receiving the notification then the giving task will continue to run, because it has the highest priority.
If the priority of the task giving the notification is lower than the priority of the task receiving the notification then the receiving task will start running the moment the notification is received.