https://bugs.winehq.org/show_bug.cgi?id=55771
--- Comment #5 from François Gouget fgouget@codeweavers.com --- MR!3959 says it is used by some .Net apps for theming purposes (I wonder how those deal with old Windows versions). Also 1903 is 4.5 years old already so if we don't add ShouldSystemUseDarkMode() now we will probably need to in a few years.
The test needs to skip it on old Windows versions though. Maybe one way is to skip if the registry key does not exist:
Version Light? w10 1507 not set w10 1607 not set w10 1709 not set w10 1809 not set w10 1909 not set w10 2004 no w10 2009 no w10 21h1 no w10 21h2 no w10 22h2 no w11 21h2 yes
All we would miss is 1909 which should have a working implementation. But that does not seem like a big issue,
Also the reason 1909, 1909 and 2009 all look alike (see comment 3) is that they all use dark mode. Since I definitely did not the light/dark mode (is that a Windows install question? If so I would have picked the default... if any) the default is probably dark... unless it's all inherited from 1507 because of the upgrades: I upgraded w1064 from 1507 to 1607 to 1709, etc. Windows may have preserved this setting through the all upgrades. However w10pro64 is a 2004 install and is dark too so I think all Windows 10 versions default to dark mode. Windows 11 however is light by default.
Alternatively one could check the Windows version but that should be a last resort.