Why does the texture look different in the scene and in the game ?
Looks largely like scaling in this case.
Could be color space, lighting, tinting, pretty much any one of ten billion other ways that textures can be modified before display.
It looks like you changed the game extension to a small value
But judging from your screenshots, the problem is not in this. I once tried to achieve a similar result by adding a render texture to the camera, but I doubt that you “accidentally” did it. However, it wouldn’t be a bad idea to tweak your camera settings.
that RT seems likely ^
check also sprite import settings,
max size (if have limited it), filtering (use point), compression (use none or color format rgba32)