From the blog:

"if your primary device is inactive for a long period, we automatically log you out of all companion devices."

There is one primary device, and multiple linked companion devices. This is different from telegram where there is no primary device.

Also see : https://faq.whatsapp.com/653480766448040

"Not all messages and chats are synced to linked devices from your phone. WhatsApp Desktop syncs more message history than WhatsApp Web. To see or search your full history, check your phone."