> and the download page looks like this: https://sourceforge.net/projects/celestia/

The page that states "Please do not download Celestia from this repository. This repository has been abandoned, and the new source and website are here and here, respectively." for the past four years ?

Try: https://celestiaproject.space/download.html and https://github.com/CelestiaProject/Celestia for version 1.6.4

Both Celestia and Stellarium have "open data" file formats that come "standard" with downloads and "extra" from community forums - ie all manner of real and SciFi movie/novel objects can be added with name, bitmaps, orbits, etc.