@pkouame your debugging is clever and sharable by most, but listen this weird experiment I did some weeks ago:
Since as known on unsupported Macs the Mojave "dark mode" QE/CI transparencies work fine, maybe for the GL coding best fitted, while in "light mode" the transparencies are flat greyed (except Notification Center and few others),
I swapped/renamed the SystemAppearance .CAR and obtained in system preferences that when I select "light mode" Mojave turned in "dark mode" and vice versa.
I don't remember exactly but I did something like renaming one in the other and vice versa:
GraphiteDarkAquaAppearance —> GraphiteAppearance
DarkAquaAppearance —> Systemappereance
AccessibilityGraphiteDarkAquaAppearance —> AccessibilityGraphiteAppearance
AccessibilityDarkAquaAppearance —> AccessibilityAppearance
And some others Vibrant I guess.
Anyway