WhatsApp was previously not able to be used on two devices with the same account logged in, but the new feature of WhatsApp will allow the users to log into two different smartphones at the same time. Moreover, the chat history from the first smartphone can also be synchronized. A report from WABetaInfo states that WhatsApp is performing a test on the app to check whether it is able to run on two different devices simultaneously or not.
However, one of the ways to connect two devices on WhatsApp was through WhatsApp Web, where you have to scan the QR code and run WhatsApp on your desktop. But, WhatsApp Web requires to be constantly connected to your cell phone, and your phone should also have a constant yet stable internet connection.
Yes, it's the ability to use your WhatsApp account from 4 devices at the same time.— WABetaInfo (@WABetaInfo) June 12, 2020
Under development, but it's great!
However, the requirements of WhatsApp to connect to other devices are entirely different, as you won’t have to keep both the devices connected. Users will be able to use a single WhatsApp account on 4 different devices at the same time. WABetaInfo tells the users that WhatsApp will release a long-rumored application for iPad too as soon as the multiple device support feature is completely ready.