WhatsApp has started testing a Wear OS 3 app for devices such as the Pixel Watch and Galaxy Watch 5.
The app displays a list of recently used contacts, and after opening a conversation, you can scroll to see previous messages. You can reply by recording a voice message or opening the system keyboard. In group chats, you can scroll to the end to see people in the conversation and open it on your phone.
You can sign up for the beta now. Both your Android phone and watch should be running at least version 2.23.10.10 to access the app.