Content aware fill. Could not fill because there are not enough source pixels on the selected layer.

Hi

I would use croping tool with content aware filling option

first crop the image to the subject and then crop again with contant aware

Working with a single sample for seamless background extension in Photoshop can be challenging, especially if the content-aware tools aren’t cooperating due to the limited texture. Here are a few suggestions that might help:

1. **Clone Stamp Tool:** Use the Clone Stamp tool to manually sample parts of the texture from your existing background and paint it onto the areas you want to fill. This method might take time but can be effective in creating a seamless blend.

2. **Duplicate and Transform:** Duplicate the texture you have and use various transformation tools (like Scale, Rotate, Flip, etc.) to position and blend it across the background. Layer masks and blending modes can help blend the edges for a more seamless look.

3. **Texture Blending Modes:** Experiment with different blending modes (like Multiply, Overlay, Soft Light, etc.) to blend your texture layer with the existing background. Adjust opacity and layer masks to control the effect.

4. **Manual Patching:** Break down your single sample into smaller sections and use them strategically to patch up the background. Blend and feather the edges for a seamless transition.

5. **Third-Party Plugins:** Consider using third-party plugins or tools specifically designed for seamless texture extension or background filling. Some plugins might offer better algorithms or techniques for this task.

Remember, achieving a seamless result might require a combination of these methods and some manual tweaking. Patience and experimentation are key when working on complex texture filling tasks in Photoshop.

I guess it depends on what you're trying to achieve. Here's my favorite of the 3 results I got with Generative Fill:

You could:

1) Make a seamless repeating pattern tile from the original, however, as it is small there will be a lot of repetition

or

2) Render your own full sizd background using clouds/difference clouds, blur, noise etc.

I wasn't expecting this!  I am not sure if this is a random shape and I am being exposed by some sort of Rorschach psychology, or it really is a silhouette of a lady with big hair eating a lolly?  Either way, I would not have been using Gen Fill to get the texture to fill the entire document area.  Content Aware Fill would be my choice. Ctrl click the texture layer to select it.  Invert the selection and expand it a bit, then use CAF

With what we are seeing, you'd remove the mystery shape from the source pixels

You might try Generative Fill instead. Select the square, invert the selection (Select > Inverse), and click on Generative Fill in the Contextual Task Bar and without adding a prompt click Generate.