Open regedit.exe,
go to Computer\HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Themes\Personalize and set both AppsUseLightTheme & SystemUsesLightTheme DWORDs to 0.
Alternatively, download and save the windows-dark-mode.reg file below as a .reg file and run it.
Source: https://old.reddit.com/r/Windows11/comments/o1l55u/how_do_i_enable_dark_mode_on_windows_11/h21f69b/
@threepointonefouronefive I understand. If this happens on Windows 11 Home, so why not upgrade to Windows 11 Pro? Many generic keys to upgrade to the Pro version can be found online. The key that worked for me was VK7JG-NPHTM-C97JM-9MPGT-3V66T.
I used that key more than 5 years ago and to this day I still use Windows 11 Pro; updates from Windows Update have arrived normally.
Here you'll find more keys https://gist.github.com/ThiagoBarradas/e21d09bdc896892299af0b21e43f1069?permalink_comment_id=6447237