Can't use f.lux or Night Shift. How can I work around this?

I have a mid 2011 Mac Mini running High Sierra. According to the apple help site, that model is incompatible with Night Shift. I have f.lux installed (had it for a couple of years) but it refuses to launch in High Sierra. I really like having the less blue night on the screen at night. Is there some way to work around this problem?

(Taken from user bobzippymail on a flux forum page)

delete "backgrounditems.btm" file under this path, and then restart your mac.

/Users/$your_user/Library/Application Support/com.apple.backgroundtaskmanagementagent/backgrounditems.btm

I would recommend making a duplicate of the file in case something goes wrong.