I tried the GitHub version to download DMM VR videos, but it failed with failed: unknown. I saw someone had the same issue earlier this year and you suggested upgrading to the Patreon version, so I bought the Itch.io version, but now I’m even more confused and still can’t download the videos. Could you please advise how to get it working?

The screenshot you posted is some kind of front end to a patched/pirated version of the software which clearly no longer works and is obviously not supported. If your a Patreon subscriber, you can simply download the latest Patreon version and use that. And if you have any issues running the project, simply associate your Discord account with Patreon and you'll get added to our community servers where people can help you.