Even if you successfully install an older APK on Android 4.1.2, you will likely face significant hurdles:

Older Android builds lack system-level security patches. Modern WhatsApp architecture relies on advanced encryption standards that Android 4.1.2 cannot hardware-accelerate or securely process. 2. Modern Feature Requirements

Many older phones (like the Samsung Galaxy S3 or Note 2) have active developer communities. You can often install a custom operating system like LineageOS to upgrade your phone from Android 4.1.2 to Android 5.0 or higher, restoring access to the official Play Store version of WhatsApp. 2. Switch to Lightweight Messaging Alternatives

Modern budget smartphones are highly affordable. Upgrading to a cheap device running a recent version of Android ensures complete app compatibility, data encryption, and overall digital safety. If you want to try setting this up, let me know: The exact of your phone Whether you want to keep old chats or start fresh If you are open to installing a custom ROM