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WhatsApp will now let users log into two accounts simultaneously
(news.retiolus.net)
This is a most excellent place for technology news and articles.
Dual-SIM phones are a thing and have been for a LONG time. They're not as common in the US (where I'm assuming you're from given you aren't familiar with dual-SIM phones) but even my S22 supports it, and I think even iPhones come with it stock now. A lot of people use two SIM cards for a multitude of reasons, and so many people have two numbers. Heck, some phones even support three SIM cards.
It's been out for a long time now. You have to set it up on your phone first but then you install the application on your computer, scan a QR code to link it, and at that point you can just disable notifications on your phone if you don't want them.
Even easier: https://web.whatsapp.com/