Darktable is an excellent RAW developer. I learned it without ever knowing lightroom since I was a full-time Linux home user before I got into DSLR photography. I learned by following this playlist of tutorials and am amazed at the possibilities of creative expression in the digital darkroom.

https://www.youtube.com/playlist?list=PLsks-zRRM1ZVN_g7P6ZAs...

https://www.darktable.org/