Thanks @TalkyRaptor
The missing JS files in the screenshot above don’t exist. There are similarly named files—they have hashes on them see here.
I do suspect, however, that if you are trying to run this proxy on Netlify, you are not going to have much success. Looking at the package.json shows a single start script which runs backend.js. This is not going to work as outlined in this support guide
Also note the Netlify Terms of Use Agreement which states under section 4. Acceptable Use
The Services may not be used as an open proxy or in any manner resembling an open proxy.
Which I suspect this app likely breaks.
Hosting the static content however is of course fine (e.g. the content in the views directory) you just need to sort of the filename issues outlined above.