Don't really know on what knowledge level you are now but you need 2 things before actually being able to say that the camera isn't up to your expectations.
1. Basic rules of photography
2. Knowledge about your camera and available settings & what the settings do
If we start with the graininess in the 2 sunset pics...
Both are kind of under exposed due to your choice of composition ... 50% pitch black & 50% lit sky. As the auto mode try to average the whole pic the result is in this case under exposure ... Under exposure in digital photography is known to generate noice, especially in the darker areas. Compere below pics ... the left is from the lighter sunset pic & the right from the darker even more under exposed. The right is clearly more noicy.
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If I look at the sharpness through your attached pictures they look equal ... the first is the dog.
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If you dislike the way the auto mode generate the color, contrast and sharpness you can make adjustments to your liking in the GO 4 app.
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The white balance setting here adjusts the tonality in the pic ... warm tone (yellowish) to cold (blueish).
This also affect the end color of objects. You have here a couple of presets depending on the light source,
an auto mode & a custom for you to tinker with if you dislike the auto or presets.
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If you then want to adjust the auto mode settings for sharpness, contrast or saturation
you go to Style. Here again a couple presets depending on motif & a custom to dial in
if you want to take your own decisions.
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Play around with all these settings & see what you like & what they do ... but one setting for everything doesn't exist, different settings are required depending on light conditions.
Once over this phase using the cameras "Auto modes" you can educated yourself more & traverse over to full manual settings, RAW formats, post processing & Auto exposure bracketing to squeeze out even more quality from the camera.
In the end I still want to encourage you to learn what a histogram is, how to interpret it & use it in the GO 4 app ... in that way you know before you take the picture if the Auto mode will mess thing up.
Link -->
Using a Histogram in DJI GO 4
Good luck!