To troubleshoot the issue, I rolled back to Blender 4.5. When using Blender 4.5, if I install Screencast Keys 4.2.1 for the first time, the image also becomes darkened. However, if I install the older version, Screencast Keys 4.2.0, the image color returns to normal. If I then update to Screencast Keys 4.2.1 from there, the mouse image in Blender 4.5 retains its normal color.

But if I try using Blender 5.0.1 to install Screencast Keys 4.2.0, the add-on fails to enable in the N-panel. Only version 4.2.1 can be enabled in Blender 5.0.1, but once enabled, it still results in the darkened mouse image issue.

4.2.0 (blender 4.5)

4.2.1（blender 5.0.1）