OdiakeS confirmed with me on Twitter that the final version was never released. It's just the three preview discs.
I also asked if there was still any way to obtain any of the discs, but he said that there isn't since he stopped doing doujin activities.
「neutral」について、今のところ、その3種類が全てです。まだ完成版はありません
同人活動のほうが停滞しており、なかなか再開出来ず申し訳ないです
Source:
https://twitter.com/OdiakeS/status/1356997907870670850