The problem is that your using the Itch.io version to attempt to download VR, which is not supported. Only the Patreon version supports VR downloading from R18.
The Patreon version is superior in almost every way. Multiple scraping sources, language translation, English subtitles, ffmpeg integration, downloading from R18 (while it lasts), FANZA, xCity.jp, frequent fixes and updates, etc. In addition, supporters of the project have access to our private Discord community, where people can get active help, submit bugs or feature requests, read guides/tutorials/faqs, download user created mods/scripts, and hang out and discuss other JAV related subjects.
Our supporters are very big JAV fans, so early breaking news spreads on our community very fast. I'd say almost everyone who uses the project in a serious manner is a Patreon supporter and participates in our Discord community. The community is almost as important as the software I'd say. In my humble opinion anyway!