If I understand correctly,
means the "Installers" folder. The one requirement for this folder (for a simplification of an installation) is to be at the same level as the downloaded .7z archive(s), not the Celestia app folder. But you also can specify the archive's address during installation, what's the question in the terminal:the unzipped folder
File "Celestia Origin v.12 - Core (30.10.2020).7z" not found.
Please specify the path to it without filename
So, enter the path to archives or place the "Installers" folder and downloaded .7z files at the same folder and try again.
P.S. Note that the installation script from the torrent has a bug at the installing medres and hires data on macOS, so replace the script file in the "Installers" folder with one from attachment:
If you want to install the core only you may use the original file.