The most common wve to mp4 conversion is related to export of Wondershare Video Editor projects (.wve files) to MPEG-4 video files (.mp4 files), something that is only possible with the original program or perhaps its successor product - Filmora. In any case, you will also need the original multimedia data referenced in the project, because without them it won't be possible to export the project.
Unfortunately, the trial version of Wondershare software leaves watermark on the video so only the full version is needed to have a clean video export. It is unlikely that any 3rd party app can be used to convert wve to mp4 this way.
Another program, Cyberlinker PowerDirector, also uses wve files for projects and these might be exported to MP4 format as well, but it's a completely different wve to mp4 conversion.
Open WVE file Open MP4 file
Suite of tools for video editing
All-in-one home video editor
All-in-one home video editor for Apple Mac
A discontinued video editing software replaced by Wondershare Filmora