Responses
I don’t really think it’s the art style that changed
since they still look the same, It’s the COLORING
Coloring is as important as the art style, manhwa artists have a bunch of assistants that help them. Most likely the one that is responsible for the color was changed.
I see way you mean in terms of shading and the decreased use of glitter(?) But I spent a weirdly long time checking and I genuinely believe the styles have changed.
Even the way the FL's brothers are drawn and the eyes of the ML are different.
I think the initial chapters were 'exhibition'/preview chapters to gain interest and probably from chapter 15/16 is when the new artstyle started. Likely, this will be the style that remains.
I'm not mad though Both styles have their positives and the current is still incredibly beautiful & emotive art.