@MahaB82A
If you have a JPEG and add a layer of any kind (including a Levels and Curves Adjustment Layer) , then it no longer meets the requirements for a jpeg. Doing a regular Save As will try to save the image as a PSD. You can intentionally choose jpeg, but note that the image will be flattened, meaning there will be one Background layer.
PNGs also have only one layer, although they do support transparency.
If you want transparency and layers, save as a PSD or TIFF.
Jane
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