IW4x-SP, IW4x, and IW6-Mod support ultra-wide monitors.
IW4x-SP and IW4x have the dvar r_customAspectRatio.
IW6-Mod has the dvar r_aspectRatioCustom.
The dvar can be described as follows:
Screen aspect ratio. Divide the width by the height to get the aspect ratio value. For example: 16 / 9 = 1.77
For example:
21/9 = 2.333
32/9 = 3.444
Finally, you must set the r_aspectRatio dvar to custom.