Regedit
Find and go to the HKEY_LOCAL_MACHINE > SOFTWARE > Microsoft > Windows > CurrentVersion > Themes > Personalize
For me Personalize folder is missing, if same in your case then Create new Key, Right click on Theme > New > Key (Give name Personalize)
Next Right click on Personalize folder and New > DWORD (32-bit) (Give name AppsUseLightTheme) and Set value to 0 (Right click on file > Modify)
Now perform the same steps 3 in this location: HKEY_CURRENT_USER > SOFTWARE > Microsoft > Windows > CurrentVersion > Themes > Personalize
if exists, modify and set value to 0
Restart your Lap
