Why does my Samsung A8 have such poor contrast after updating to Android 9?
You can change that.


Go to Settings -> Accessibility -> Visibilty enhancements -> then try some functions there and see what is best for you (contrast theme,contrast font etc.)
If you are using any Galaxy Theme, after system update, they are also updated, so this can alse be a problen. You should try to change or just dissable theme you are using(if you are using) for a moment to test it.
If you love Night Mode,it can also solve your problem, but it is not good for using outside.