System Information
Operating system: Windows 10
Graphics card: RX580

Blender Version
Broken: 3.0.0

The camera data node's "View Vector" output does not work under Cycles in the viewport when used in World shaders.
Note that it _does_ work as expected if there's an active camera (although it's not quite as bright as Eevee).

Eevee viewport rendering:

Cycles viewport rendering:

Cycles viewport (with active camera) rendering:

Exact steps for others to reproduce the error
Connect the camera data "View Vector" output directly to the "Surface" input of the "World Output" node.
Switch to rendered view.
Observe that the view vector is incorrect when navigating the viewport in Cycles, but correct when in "camera view" (numpad 0) or in Eevee.