Clutching at straws now - did you download Audacity via the Audacity website (https://www.audacityteam.org/download/mac/) or some other website, or build it from source?
If you try to amplify that recorded track, what happens?
Does the Amplify effect say that the "New peak amplitude" will be "-Infinity", or can you actually amplify the track?
See if VLC media player can play the DVD. If it can play it, then it should be able to "Convert" it to a WAV file.
(VLC is a free, open source media player that also has the ability to convert media to other formats: https://www.videolan.org/vlc/index.en-GB.html)
Please check the date of topics that you are replying to. If the topic is years old, then there's no point posting a reply except in the case of posting a canonical solution.
If I do a File > Import > Audio and select a .VOB file from the DVD, I get an error message that implies FFmpeg is not installed or not working properly. Try copying the VOB file to your hard drive first, then import into Audacity from the hard drive copy. If you still get an error, please tell us ...