At this point, your best bet is WhatsApp Web through an up-to-date browser like Chrome or Firefox (assuming you can still get updated versions for Windows 7, or at least a reasonably recent one). Just be cautious with any unofficial desktop app downloads claiming Windows 7 support-most are outdated or shady. If you’re after notifications or a more “app-like” feel, you could try using the “create shortcut” feature in your browser to pin WhatsApp Web to your taskbar; not perfect, but it works. Don’t expect native desktop notifications to be flawless, but it’s a decent workaround for older hardware.
