The change is detailed in a support document...
About supported operating systems
We provide support for and recommend using the following devices:
● Android running OS 4.0.3 and newer
● iPhone running iOS 10 and newer
● Select phones running KaiOS 2.5.1 newer, including JioPhone and JioPhone 2
The change is likely to affect a minimal amount of users as most are running a much newer software version. You can download WhatsApp Messenger from the App Store for free at the link below.