Forgive the screenshot taken and edited around my bedtime, but I think it illustrates the problem well enough even without much text:
To force light mode at all times:
defaults write com.apple.iCal NSRequiresAquaSystemAppearance -bool yes
To restore following system settings:
defaults write com.apple.iCal NSRequiresAquaSystemAppearance -bool no
It should work for other apps too, if you replace the iCal
part.
Credit to u/Careless-Royal-2939 on Reddit for the hot tip.
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