Have you considered using Redshift manually? Here's what I do:
First, uninstall redshift-gtk and just install redshift.
Next, according to redshift -h
The neutral temperature is 6500K. Using this value will not change the color
temperature of the display. Setting the color temperature to a value higher
than this results in more blue light, and setting a lower value will result in
more red light.
Default values:
Daytime temperature: 6500K
Night temperature: 4500K
In my case, I create custom menu items (Mint's menu editor) and link them to those scripts so I can run them from the main application menu/ add them to my dock.
Never used it but found this on the archwiki
https://github.com/jumper149/blugon.
Weird that redshift isnt working for you, it worked great for me when i used it