Hello @Chetan_Deshmukh ,
Your forward_export has not affected. If you pip install ultralytics package, you need to add forward_export in package. The right model output like this.
Then, Try convert nb
If still fail, modify onnx opset version and try convert nb again.
import onnx
model = onnx.load("./yolov8n.onnx")
model.opset_import[0].version = 12
onnx.save(model, "./yolov8n_1.onnx")
Sorry for reply late, last week we took Spring holiday. If you still convert failure, please provide your right output onnx model. I will feedback our engineer.