FLUX uses a complete different style of prompting than Stable Diffusion. FLUX wants full sentences to describe what you want (sort of) whereas Stable Diffusion mostly wants keywords.
Cool trick: You can ask ChatGPT or Gemini to convert a Stable Diffusion prompt to FLUX-style and vice versa to understand the difference. You can also give it a negative prompt and ask how you could incorporate that into a FLUX prompt 👍