I'm at my wit's end trying to get Night Light to work correctly. Any tips on how to remove it completely in Gnome 3.28.4 running on Ubuntu 18.04.5?
Settings → Devices → Screen Display → Night Light → click and set the slider as required in the second window to turn it off (or set the conditions).
As guiverc says in his comment under the OP it is easier (and safer) just to disable it as upgrades increase the chance of it re-appearing and release-upgrades causing future problems with your system. So, in short, whilst it might be possible to remove it altogether it would be best just to disable it and maintain system integrity.