You have to join the discord for the newest version. Haven't tried it yet, but I joined the channel and the link to the most recent version was posted May 1st this year (2021) and also Halloween bonus content was appended to that post May8th.
Viewing post in Monster Girl Island: Prologue comments
if you go to 'more information' above and hit the 'community' link there, it'll take you to:
https://discord.com/invite/GZEkMGe