If you like them _ultra short_ then I'd recommend 365tomorrows.com which feels like a single page ripped out of a greater (non-existent) work. Most, but not all, have a sci-fi theme.
I was surprised not to see Forster's stories as they are marvelous and public domain. People often cite the machine stops, but I recommend reading them all. The point of it and co-ordination are two favorites
https://standardebooks.org/ebooks/e-m-forster/short-fiction
https://www.libraryofshortstories.com/about
https://ko-fi.com/evanclewis