that we're unaware of

Here are things that you're now aware of:

• Stable Diffusion watermarks images to mark them as generated. Most UIs including AUTO1111 can turn this feature off
  
• Stable Diffusion embeds the text of the prompt into the image's EXIF data by default, however this EXIF data doesn't usually survive upload to social media. EXIF is where cameras place identifying data like geotags, so most social media upload UIs automatically strip this data for user safety.
  
• There are likely additional noise parameters that academic researchers can extract from an image that can tell top-tier forensic experts which model weights you used; however if top-tier forensic folks are looking at your image they probably also have metadata like "what IP uploaded this image, on what date, and what username..."

Steganography, especially cryptographically robust steganography, is capital-H hard. Don't worry about it.