As the title says, the system settings will shut down when I try to change Night Color in display and monitor settings. Now i'm stuck in night color which is very unpleasant.

I experience something similar, though system settings very often crashes for me, and as far as I can tell it's not specific to Night Color.

However I also can't change the Night Color setting because even though I uncheck the box, the Apply button doesn't enable. There is no way to apply the change.

I was under the impression (from other readings here) that you had to be running Wayland to use Night Color. However I'm not, as far as I can tell running Wayland. I don't have plasma-wayland-session installed, for instance. But best I can tell it is running, given the tint of my screen.

Additional issue: starting at 18:00 (configured Night Color sunset time) for about 30 minutes (configured Night Color transition duration) the screen has repeatedly fluctuated between daytime and nighttime color temperatures.