The themes are made with WinClassicThemeConfig Instead of creating it in 3DCC, Desk.cpl, 98 Plus! etc.

Download: https://winclassic.net/thread/1436/new-classic-theme-configurator
And finally the .reg file itself: https://gliczide.nekoweb.org/downloads/Gliczide_-_Classic_Themes.reg

For your infomation about .reg file: It doesn't even modify system itself, just adds ClassicSchemes under the path: HKCU\Control Panel\Appearance (HKCU = HKEY_CURRENT_USER) 

For W8-11+: You need to use TinyClassicTheme/Windhawk to enable classic theme