Force stop play store and clear its cache. Then try downloading WhatsApp on a stable network. I am a S21FE user too and I am not facing this issue. This is not a device specific issue. It can happen sometimes due to either Google Play Store or app installer misbehaving.
Thank you for sharing your concern. And please follow the easy troubleshooting steps which might help to solve the issue.
Clearing the app cache is kind of like a cleanse for your apps. It will get rid of residual files that could be slowing down the app. Open Settings, and then swipe to and tap Apps. Select or search for the app you want to clear. Tap Storage, and then tap Clear cache.
However, we would request you to register your concern in Samsung Members Application. So, that our concern team gets back to you as soon as possible.
Please follow this path to register your concern in Samsung Members Application (Open Samsung Members Application > Get help > Send Feedback > Error report).
Thank you for writing to Samsung. Warm regard, Samsung customer support
