You'll need to follow the latest instruction provided here.
https://7thbeat.notion.site/Neo-Cosmos-itch-io-install-guide-916eb8eb93c748eca42...
7BG changed the way that Neo Cosmos should be installed since April this year.
In short, for Windows, create a folder named NeoCosmos at the place where A Dance of Fire and Ice exe is located. Then, put the StandaloneWindows (for Win 32-bit) or StandaloneWindows64 (for Win 64-bit) in that NeoCosmos folder.
You can refer to the link above or the download page for the instruction of download. (for both Windows and Mac)
After following that instruction, run the game and you should be able to enter the Neo Cosmos portal.