Shadow seen on the model

In this model, a shadow is formed as seen in the picture. I couldn’t find the reason. It is not visible in other corners. What would be the reason?
Thank you.

test.skp (333.6 KB)

It’s an unfortunate artifact of smoothing that happens with flat faces. It can work better to use hide edge rather than smooth edge.
You can see here, ctrl with eraser gives the ‘shadow’ but shift with eraser doesn’t.
GIF 8-12-2023 12-30-54 AM

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Also, try this…

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Thank you all!