Is there a reason why the compile datetimestamp from Serial Report isn't sufficient here?

this is almost trivial

When BUILDDATE is defined add a submenu "Build Datetime" to the About Printer menu
This menu shows the build date and time
I didn't want to add it to the Printer info menu, as there is already a release date and time in there and it was just confusing.

Eg added submenu

The build date and time

diff --git a/Marlin/Configuration_adv.h b/Marlin/Configuration_adv.h
index 564f44df60..f992dd7884 100644
--- a/Marlin/Configuration_adv.h
+++ b/Marlin/Configuration_adv.h
@@ -1546,8 +1546,9 @@
   #endif
 
   // Include a page of printer information in the LCD Main Menu
-  //#define LCD_INFO_MENU
+  #define LCD_INFO_MENU
   #if ENABLED(LCD_INFO_MENU)
+    #define BUILDDATE
     //#define LCD_PRINTER_INFO_IS_BOOTSCREEN // Show bootscreen(s) instead of Printer Info pages
   #endif
 
diff --git a/Marlin/src/lcd/menu/menu_info.cpp b/Marlin/src/lcd/menu/menu_info.cpp
index 2db0caa805..81ca11beca 100644
--- a/Marlin/src/lcd/menu/menu_info.cpp
+++ b/Marlin/src/lcd/menu/menu_info.cpp
@@ -263,6 +263,18 @@ void menu_info_board() {
 
 #endif
 
+//
+// "Build Date" submenu
+//
+#if ENABLED(BUILDDATE)
+  void menu_info_build() {
+    if (ui.use_click()) return ui.go_back();
+    START_SCREEN();
+    STATIC_ITEM_F(F(__DATE__ " " __TIME__));
+    END_SCREEN();
+  }
+#endif
+
 //
 // "About Printer" submenu
 //
@@ -306,6 +318,11 @@ void menu_info() {
   }
   #endif
 
+  #if ENABLED(BUILDDATE)
+    SUBMENU(MSG_INFO_BUILD, menu_info_build);
+  #endif
+
+
   END_MENU();
 }
 

Everything needs a define, so it can be removed entirely from the code.

This is awesome.
Just wondering, on which version of configuration/configuration_adv.h is the 'diff' based upon?
I'm using 'configs' of Marlin 2.1.2.4 with BTT-SKR-Mini-E3/BTT TF35 and can't locate the spots so easily in my files.
Thanks for the suggestions.

based on bugfix 2.1.x

this is for marlin menus, to update the touch interface would require you to update the btt tft firmware

I have created a PR to add this

based on bugfix 2.1.x

I figured out where it has to go.
The only problem is (and I'm not a c++ guru) I'm receiving an error when compiling 'Marlin/src/lcd/menu/menu_info.cpp: In function 'void menu_info_board()': Marlin/src/lcd/menu/menu_info.cpp:232:5: error: a function-definition is not allowed here before '{' token
and later on as consequence of that
Marlin/src/lcd/menu/menu_info.cpp:333:29: error: 'menu_info_build' was not declared in this scope; did you mean 'menu_info_board'? 333 | SUBMENU(MSG_INFO_BUILD, menu_info_build); // Printer Stats >
So at the moment I'm stuck with that. Too bad.
Any help is much appreciated even though its not really a problem of the Marlin code.
TIA

Update:
I figured it out.
I positioned the changes at the wrong spot in "menu_info.cpp".
After I consulted the original file from bug-fix 2.1.x, I changed the location (to the right spot), and now it's compiling w/o any error.
Have to flash the firmware and see how it looks on the display.
Thanks again for all feedback.