Many people don't know that Microsoft kept the Windows 7 activation servers online for nearly a decade after end-of-life (which was Jan 14, 2020). You can still purchase a legitimate Windows 7 Pro key from authorized resellers (or sometimes find old stock). Alternatively, if you have a Windows 7 sticker on your old PC, simply reinstall Windows 7 and enter that key. It will likely still activate.
: It removes the activation requirement rather than simulating a valid key, effectively disabling the "non-genuine" notifications and prompts. RemoveWAT 2.2.6 All Windows Activator -Specially for Win 7-