https://pcgamingwiki.com/wiki/Halo:_Combat_Evolved#Mouse_wheel_activates_other_background_windows As of dgVoodoo W.I.P 51, dgVoodoo has become capable of wrapping DirectX9 games to DirectX 11 via D3D9.dll. This means we can now use dgVoodoo's mouse capture, which prevents input such as scrolling from applying to applications which are out of focus. This sort of thing is easiest to test on a multi-monitor setup.
Link for dgVoodoo WIP releases: dege.freeweb.hu/dgVoodoo2/dgVoodoo2.html
Link to changelog from WIP60_1: pastebin.com/nmgFPtzh
(I can't post hyperlinks or else reCaptcha will get stuck in a loop again.)