Windows Phone 8.1 requires PC software deployment tools because the native file manager cannot execute XAP installations without an active Store connection.
The app is pulled from the application store, preventing new downloads. This can be bypassed by sideloading a XAP file.
The Complete Guide to Downloading WhatsApp XAP Files for Windows Phone
The Complete Guide to Downloading WhatsApp XAP Files for Windows Phone download whatsapp xap file for windows phone
Operating systems use specific file formats to package and install applications. uses APK files. iOS uses IPA files. Windows Phone (8.0 and 8.1) uses XAP files.
You will need the Windows Phone Application Deployment Tool (part of the Windows SDK).
If your device does not support SD cards, you will need to use the via USB (described in the "Enabling Sideloading" section above). Windows Phone 8
how to install .xap file in windows phone 8 - Microsoft Learn
To install a .xap file, your phone cannot be restricted. You need the following:
Unofficial mirrors may host broken or incomplete application packages that can cause your device to boot-loop or crash. How XAP Deployment Works (For Archival Purposes) The Complete Guide to Downloading WhatsApp XAP Files
Your specific and OS version (Windows Phone 8.1 or Windows 10 Mobile) If your device is already interop-unlocked
I can provide the specific step-by-step guides or tool links for your exact setup. Share public link