Most operating systems have one built in. Is there a feature missing from yours?

That should be built into the OS, if you’re on anything relatively recent.

If you are using kde plasma

https://userbase.kde.org/Tips/Enabling_the_blue_light_filter_on_KDE_Plasma

Maybe Redshift?

Redshift?

BTW for Android, there are 2 kinds of blue light filters, both are available on F-Droid:

• Those that recalibrate the display via KCAL. If your OS has one built in, it’s almost always one of these. If it doesn’t, root is required to install it. These generally yield better results because they take gamma into account and can theoretically maintain color depth (depends on the display). Don’t worry about possibly miscalibrating your display, it most likely doesn’t have non-volatile memory so uninstalling the app and restarting your phone will turn it back to normal. Recommended: Night Light
• Those that display a fullscreen overlay. Root is optional but you cannot cover the keyboard and status bar without it on modern Android versions (and hide the overlay from screenshots), and old ones don’t support multichannel alpha so a color filter will actually make dark areas lighter. However, if you’re a root user of Android 10 (and maybe some older versions I didn’t test), the filter works perfectly. Recommended: Red Moon

Could ask the foss community as well since most open source software is privacy friendly by nature