You could try publishing on popular online platforms like Kindle Direct Publishing or Wattpad. They have a wide reach and attract a lot of readers.
Traditional publishing houses that focus on speculative fiction are also a good option. For example, Tor Books or Orbit Books. They have experienced editors and marketing teams that can give your work more visibility. However, getting accepted by them can be quite competitive.
Some indie publishing companies specifically for speculative fiction might be worth considering. They offer more flexibility and might be more willing to take risks on new authors. But you need to do your research to find the ones with a good reputation and distribution channels.