Since you are on Android 7.1.1, you need to allow app installation from outside the Play Store:
If you see the message "Your device isn't compatible with this version," do not panic. This sometimes happens due to a Play Store caching error. Proceed to Method 2. Download Whatsapp For Android 7.1.1
Do not download APKs from random websites. Only use trusted mirrors: Since you are on Android 7
In conclusion, downloading WhatsApp for Android 7.1.1 is entirely feasible, but it exists in a grey zone between supported and optimal. For the average user, a simple visit to the Google Play Store will suffice, delivering a stable, if slightly feature-limited, version of the app. For the more determined user willing to sideload, success depends on meticulous attention to architecture and source legitimacy. However, the decision to continue using Android 7.1.1 for WhatsApp is ultimately a trade-off: convenience and familiarity at the cost of future feature updates and robust system security. As WhatsApp inevitably raises its minimum requirements to Android 8.0 or higher—a change that is likely within the next 12 to 18 months—users on 7.1.1 will face a hard choice: upgrade their hardware, or be left behind in the silent graveyard of unsupported software. Until that day arrives, with caution and correct procedures, the conversation can continue. Do not download APKs from random websites
