Rovio officially discontinued support for the PC versions of their classic games years ago. In many cases, the activation servers that verify these keys are no longer online.
: You can still find installers for version 4.0.0 on community archives or third-party sites like Internet Archive Common Community Methods angry birds 4.0.0 activation key for pc
Version 4.0.0 uses a simple HTTP GET request to proxy.rovio.com for verification. Rovio officially discontinued support for the PC versions