[Hwenray]

Hmm, it's a bit hard to tell from the photo (not your fault, taking a photo of the screen never looks like it does irl in my experience), but there is a subtle gradient background on the inbuilt dark theme that may be causing or making the banding more apparent. You could try a theme with a flat background (such as Ayumi's theme from https://codeberg.org/cool-tech-zone/tangara-themes), and see if that helps, or if it at least makes it easier to tell whether it's an issue with the display itself or with the gradient rendering.

It worked, thank you for your reply!!!
The gradient rendering is gone when I switched to the Ayumi's theme.