Enabling Night Light permanently on Ubuntu 20.04

Solution 1:

I'm not aware of any simple command line alternative, but you can keep Night Light on throughout the (24 hours) day using the Night Light Slider GNOME Shell extension. Its main purpose is to add a slider to the system menu to control Night Light's colour temperature:

But it also provides an option to enable Night Light all the time ('Enable always'):

This option actually periodically changes Night Light's schedule under the hood in order to keep it activated all the time.

P.S. Refer to this Q&A to learn about installing and managing GNOME Shell extensions: How do I install and manage GNOME Shell extensions?