Samsung mobiles use the Tizen OS, and the Tizen Store instead of the Google Play Store. As of October 2020, WhatsApp is no longer available on the Tizen Store because it is not supported on Tizen OS. Evidently, you can also no longer update WhatsApp in the Tizen Store. You must switch to another compatible device to use WhatsApp. Or alternatively, there is IMO, which is similar to WhatsApp.