How to convert a single safetensors file to PEFT format

No conversion needed. Use it directly with Diffusers like this:

https://huggingface.co/lightx2v/Qwen-Image-Lightning :

pipe = DiffusionPipeline.from_pretrained(
    "Qwen/Qwen-Image", scheduler=scheduler, torch_dtype=torch.bfloat16
).to("cuda")
pipe.load_lora_weights(
    "lightx2v/Qwen-Image-Lightning", weight_name="Qwen-Image-Lightning-8steps-V1.0.safetensors"
)