Not to be outdone by Telegram's new "Mark as read" button on notifications, WhatsApp is rolling the same feature out to some users now. Not everyone is able to see this shortcut, even those of us on the latest beta, so it appears the function is enabled via a server-side switch.
We've received several reports from users on the most recent beta v2.18.232 who are seeing this new "Mark as read" option on WhatsApp notifications. Tapping it does exactly what it should: it dismisses the notification and marks the message as read so it doesn't resurface when you open the app or get another notification. And we love it for exactly the same reason we love the Telegram one — it's very handy.
To see if you have it, make sure you're on v2.18.232 beta, which you can grab from the Play Store or from APK Mirror, and check your notifications. If you're one of the lucky ones, the option will be there. If not, join me in praying to the server-side gods that it gets enabled for all of us soon.