Why is celery task status always pending?

Question

Flask

Mastering celery+flask. It seems that everything is set up, both backend and broker, the result of the task returns normally, but the state is constantly PENDING. Why is that, and how to fix it? I searched on stackoverflow and other sites, the only suggestion is to use the --pool=solo flag when initializing the cellery, but then the meaning of celery is lost, because with --pool=solo all tasks are executed in one thread.