The dark-light almost horizontal bands of the first image could be the "amp-glow" that you read about. It eminates from a warm spot on the sensor.
Amp glow is usually removable by taking dark frames at the same sensor temperature, and at the same expsoure time and camera gain. I don't believe your camera has a cooled sensor, so using an arbitrary dark frame (taken at a different temperature) can make the problem worse instead of helping.
If you cannot switch to a different camera, you can try taking dark frames right after taking your light frame, so that the temperatures are somewhat similar.
The color gradient in the second image is quite likely (with the light pollution nowadays) to be from the pollution gradient in the sky. When you took that image, the left side of the image was not closer to the horizon, was it? Or in a direction that is closer to city lights.
The right side is nice and dark and could be away from city lights, or closer to the Zenith, or wait for M45 to move to that darker part of the sky to look for nebulosity. If the sky background is brighter than the nebulosity, it is close to impossible to bring out the nebulosity (SNR-wise).
Better light pollution filters can help a little, but if you have uneven pollution, there is not much you can do about it except to move to a different location. And if the filter cuts too much blue region, the M45 nebulosity will be cut too. You just have to wait until the object has moved to a different part of the sky (like up closer to Zenith) that is not polluted, or has less gradient.
Otherwise, there are tools that can be quite effective in removing sky gradients, like on AstroPixelProcessor:
https://www.astropixelprocessor.com/community/main-forum/gradient-and-noise/
I don't know what error the third image is showing. I simply see some clumps of uneven illumination. Could be attributable to a poor sensor that is not meant for long exposures. I also see an almost-horizontal band in the nebulosity below the horse's head. I just looked at an image that I took some time back, and that band is not present, so it is something from the camera:
![](https://bbs.astronomy-imaging-camera.com/assets/files/2023-02-05/1675636481-948484-horse.jpg)
Did you check to see if is not some finger oil smear across a part of the long edge of the sensor? Dark frames will not be able to remove a defect like that.
Perhaps check what an ad-hoc flat frame shows (i.e., just a simple unsaturated daytime image with a T-shirt). If it is not a 100% opaque obstruction, a good set of flat frames (taken at any temperature and exposure value) will mostly fix the problem, albeit with a loss of SNR in those smeared regions.
Chen