WhatsApp 2.23.10.5 is the last version with a green icon that does not show the 'Outdated' label. Meta is pushing a new Windows Store version of WhatsApp Desktop in replacement of the legacy desktop app which now says 'Outdated' in the window title, however the new version is still missing features and some do not like the new look.
Why does WhatsApp Desktop say 'Outdated'? After signing up, your phone doesn't need to stay online to use WhatsApp on linked devices, but your linked devices will go offline if you don't use your phone for more than 14 days. You only need your phone to be online when you register WhatsApp for the first time or pair new devices. You can use up to four linked devices and one phone at a time. The messages you send and receive are synced, and you can see your messages on all devices seamlessly. Yes, WhatsApp web and desktop applications are extensions of the WhatsApp account on your phone. Can I use WhatsApp on my computer and phone at the same time? The messages you send and receive are synced between your phone and computer, and you can see your messages across all devices.
WhatsApp for Windows and Mac are extensions of the WhatsApp account on your phone.