This simple LoRA produces unibrows on portrait faces. I couldn't find others that did it, so I trained (though with some really crusty training images).
Notes:
Works better with Euler/Euler Ancestral scheduler;
Higher weights alters the face;
The face might be preserved if using IPAdapter or Inpainting;
The Inpainting works better at lower denoise;
If the FaceID (IPAdapter) is too strong or is set to be totally linear for all steps, the LoRA might not have any effect since the face will override it.
Setting the FaceID to 'ease in-out' or similar helps;
Mid values might alter the background if that isn't specified in the prompt;
If the unibrow has too much contrast, refining with a lower weight or using another scheduler might mitigate it;
Adetailer/Face Detailer might also help getting better results;