On March 4, Apple informed developers that all new apps submitted to the App Store would have to comply with the updated App Store Review Guidelines. The guidelines were changed to include features introduced with iOS and iPadOS 13 SDK or later. These changes pertain to reviews, spam, push notifications, Sign in with Apple, data collection and storage, mobile device management, and more.
All apps already on the store needed to be updated accordingly. The deadline to update the existing apps was previously April 30, 2020.
On March 26, Apple extended the deadline to update their apps on the App Store. It has now been moved to June 30, 2020.
The announcement simply states that this is to “accommodate developers who may need additional time.” In all probability, it has to do with the COVID-19 pandemic, which forced many devs to switch to remote work or even suspend certain processes.
The full text of the updated App Store Review Guidelines that apps will have to comply can be found here.