The problem has been going on since 2013. In iOS 14.5, Apple said that they fixed the problem with receiving mail. On March 29, the APNS certificate was updated, but this did not solve the problem. If my Internet is turned off, I receive an email to iCloud mail in the standard mail app, including the Internet, when I wake up in the morning, I do not receive notifications. I need to open the mail manually and pull the screen down. If a new email arrives during the time when the Internet is turned on, it pushes through the old notification and a new one comes out. In 2021, push doesn't work for Apple mail.