You can try the things we've described over here:
https://groups.google.com/g/video-downloadhelper-q-and-a/c/sNfTCMYfiTU
Or you can look over here:
https://groups.google.com/g/video-downloadhelper-q-and-a/c/BzPLK2YyL-s
Look for the discussion of video without audio.
But correct me if I'm wrong. Dropbox is not a producer of multimedia content. Rather,
Dropbox is a place that offers free disk space where people can upload anything they
want, and then share it with whoever they want. It's basically the same thing as Google
Drive, no? So if the content on Dropbox is faulty in some way, that's the fault of
whoever did the upload. If this is not private or sensitive content, perhaps you could
post a link & I'll take a look at it.