Convert IFO to WAV

It is not possible to directly convert DVD-Video Disc Information Files to WAVE Audio Files (.ifo to .wav conversion). IFO files do not contain any media data, merely information data, and are only useful as complete video data files in conjunction with VOB and VRO files.

Once you have the entire set of files (IFO, VOB, VRO), you can convert those to a single video format, such as MP4.

Then you can easily convert MP4 to WAV.

Simply put, it is impossible to convert IFO to WAV directly.
Thus, there is no so-called ifo to wav converter or a free online ifo to wav converter to be found.