⚡️ E3V2 blank bg for S1 compatibility (#23822)

Marlin/src/lcd/e3v2/marlinui/dwin_lcd.cpp

@@ -45,6 +45,7 @@ void DWIN_Startup() {
   const bool success = DWIN_Handshake();
   if (success) DEBUG_ECHOLNPGM("ok."); else DEBUG_ECHOLNPGM("error.");
   DWIN_Frame_SetDir(TERN(DWIN_MARLINUI_LANDSCAPE, 0, 1));
+  DWIN_JPG_ShowAndCache(3);
   DWIN_Frame_Clear(Color_Bg_Black); // MarlinUI handles the bootscreen so just clear here
   DWIN_UpdateLCD();
 }