Users can continue to use the application by clicking 'OK' after seeing the notification. This means that Apple's watchOS 4.3.1 is still compatible with these old versions of the application. This is similar to the notification that Apple stopped pushing support for 32-bit applications.
For developers, this is not new. As early as last November, Apple has announced that it will no longer accept applications based on the watchOS 1 SDK since April 1, 2018. When Apple asked developers to update existing applications, You must use the watchOS 2 SDK framework above. Newly submitted applications must use the watchOS 4 SDK framework.
Although older applications can still run properly on watchOS 4.3.1, foreign media believe that in the future of watchOS 5, these applications will be completely stopped.