The rejection reason was probably “Quality Issues”. You should always share this with us, when submitting a request for comments. The header is enough. But as most of the friendly contributors here do not speak Korean, it would be nice to copy and paste as a text (품질 문제) so that the translation works.
You have artefacts (1) and aliasing (2) everywhere where you look at.
It is not possible (or only with a high expenditure) possible to correct this.
In addition:
The DPI (PPI) value is irrelevant.
As for the marking that an asset is generative AI, it is enough to mark it with the corresponding tick marks before submitting.
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ABAMBO | Hard- and Software Engineer | Photographer