Windows Classic theme on Windows 11 and Windows 10 1903+

Regarding changing the theme, the best is to use themes.exe, as clara indicates.
Your configuration is good overall.
However, I think you forgot:
- To disable the ribbon in Explorer, the ribbon is poorly displayed with the classic theme (it is possible to deactivate it with ExplorerPatcher or a Windhawk mod).
- To display with Open-Shell a start button
- To activate Syslistview32 in the explorer (this is possible with ExplorerPatcher or a Windhawk mod).
On the other hand, the buttons seem to be displayed incorrectly in the taskbar. You can replace the Classic Taskbar Fix Lite mod with this mod (this is the same mod that I modified to remove the space between the icons, which corrects the display problem) :
// ==WindhawkMod==
// @id              classic-taskbar-buttons-lite-wtis
// @name            Classic Taskbar 3D buttons Lite VS - Without icon spacing
// @description     Lightweight mod, restoring the 3D buttons in classic theme
// @version         1.1.1
// @author          Anixx
// @include         explorer.exe
// @compilerOptions -lgdi32 -lUxTheme
// ==/WindhawkMod==

// ==WindhawkModReadme==
/*
# Classic Taskbar Fix
Restores 3D buttons on taskbar when using Windows Classic theme. Based on mod by Aubymori (https://github.com/aubymori).
*/
// ==/WindhawkModReadme==

#include <windhawk_utils.h>
#include <windows.h>
#include <uxtheme.h>
#include <tmschema.h>


typedef struct tagBUTTONRENDERINFOSTATES {
   char data[12];
} BUTTONRENDERINFOSTATES, *PBUTTONRENDERINFOSTATES;

/* Remove clock hover effect */
typedef void (* GDIHelpers_FillRectARGB_t)(HDC, LPCRECT, BYTE, DWORD, bool);
GDIHelpers_FillRectARGB_t GDIHelpers_FillRectARGB_orig;
void __cdecl GDIHelpers_FillRectARGB_hook(
   HDC     hDC,
   LPCRECT lprc,
   BYTE    btUnknown,
   DWORD   dwUnknown,
   bool    bUnknown
)
{
   return;
}

/* Draw taskbar item */
typedef void (* CTaskBtnGroup__DrawBar_t)(void *, HDC, void *, void *);
CTaskBtnGroup__DrawBar_t CTaskBtnGroup__DrawBar_orig;
void __cdecl CTaskBtnGroup__DrawBar_hook(
   void *pThis,
   HDC   hDC,
   void *pRenderInfo,
   PBUTTONRENDERINFOSTATES pRenderStates
)
{
   LPRECT lprcDest = (LPRECT)((char *)pRenderInfo + 4);

   HTHEME hTheme = OpenThemeData(NULL, L"BUTTON");

   if (hTheme) {
       int iStateId = PBS_NORMAL;

       if (pRenderStates->data[2]) {

           iStateId = PBS_PRESSED; // or use PBS_HOT if you prefer

       } else if (pRenderStates->data[4]) {

           iStateId = PBS_PRESSED;

       }

       // Draw the button with the current theme.

       DrawThemeBackground(hTheme, hDC, BP_PUSHBUTTON, iStateId, lprcDest, NULL);


       // Close the theme data handle when done.

       CloseThemeData(hTheme);
   } else
   {
       // Fallback to non-themed drawing if themes are not available.

       UINT uState = DFCS_BUTTONPUSH;
       if (pRenderStates->data[2])
       {
           uState |= DFCS_CHECKED;
       }
       else if (pRenderStates->data[4])
       {
           uState |= DFCS_PUSHED;
       }

       DrawFrameControl(hDC, lprcDest, DFC_BUTTON, uState);
   };


   /* If button is pushed in, offset the rect for the icon and text draw */
   if (pRenderStates->data[2]
   ||  pRenderStates->data[4])
   {
       lprcDest->top++;
       lprcDest->bottom++;
       lprcDest->left++;
       lprcDest->right++;
   }

   return;
}

BOOL Wh_ModInit(void)
{
   HMODULE hExplorer = GetModuleHandleW(NULL);

   WindhawkUtils::SYMBOL_HOOK hooks[] = {
       {
           {
               L"void __cdecl GDIHelpers::FillRectARGB(struct HDC__ *,struct tagRECT const *,unsigned char,unsigned long,bool)"
           },
           (void **)&GDIHelpers_FillRectARGB_orig,
           (void *)GDIHelpers_FillRectARGB_hook,
           FALSE
       },
       {
           {
               L"private: void __cdecl CTaskBtnGroup::_DrawBar(struct HDC__ *,struct BUTTONRENDERINFO const &,struct BUTTONRENDERINFOSTATES const &)"
           },
           (void **)&CTaskBtnGroup__DrawBar_orig,
           (void *)CTaskBtnGroup__DrawBar_hook,
           FALSE
       },
   };

   if (!WindhawkUtils::HookSymbols(hExplorer, hooks, ARRAYSIZE(hooks)))
   {
       Wh_Log(L"Failed to hook one or more functions");
       return FALSE;
   }

   return TRUE;
}