How to use one WhatsApp account on four devices?

Unfortunately, WhatsApp currently does not allow users to use one account on multiple devices simultaneously. However, WhatsApp is reportedly working on a feature called "multi-device support" which will allow users to use the same account on up to four devices.
Once this feature is rolled out, you will be able to use the same WhatsApp account on four different devices without having to log out and log in each time you switch devices. It's important to note that this feature is not currently available and there is no official release date at this time.

In the meantime, if you want to use your WhatsApp account on multiple devices, you can use WhatsApp Web on your desktop or laptop, or use the WhatsApp app on a secondary phone or tablet. However, you will still need to have your primary device connected to the internet and logged into WhatsApp for these options to work.

Go to Your web browser and write in the address bar https://web.whatsapp.com/.
Open WhatsApp on your primary device and tap the three-dot menu in the top right corner.
Select "WhatsApp Web" from the menu.
Scan the QR code on the WhatsApp Web page with your phone to link your WhatsApp account to your computer.
now use WhatsApp on your computer without installing software.
Here's how to use WhatsApp on a secondary phone or tablet:

Download and install WhatsApp on the secondary device from the app store.
Open WhatsApp on the secondary device and enter your phone number to verify your account.
You will receive a verification code via SMS or phone call. verify your account with this code.
You can now use WhatsApp on your secondary device. Keep in mind that your primary device must be connected to the internet for this to work.
Note that using WhatsApp on multiple devices in this way may result in a degraded experience, as some features such as end-to-end encryption may not work as intended. It's also important to keep your account secure by enabling two-factor authentication and not sharing your account information with others.