Here is a link to a website that has become an archive of DLC modifications consisting of enhancements to routes, reskins, sounds, lights for rolling stock, and locomotives from various sites that have closed or a bit shaky. I have used several of these and most are well done and work "out of the box". Be aware they may be no longer supported by their original developers. Use at your own risk and make backups. Be sure to read the readme file and make sure you have all of the dependencies needed prior to installation of any of these enhancements.
https://sites.google.com/view/train-simulator-mod-archive/home
Mission Statement:" Who We Are: We are a dedicated community committed to preserving the legacy of Train Simulator mods. As the virtual landscape of Train Simulator evolves, many websites hosting invaluable mods are unfortunately facing the threat of closure, putting years of creativity and passion at risk of being lost forever."