This method which I don't recommend unless you want go through with it without help from XP script. (Not sure if RGSS for this exist yet)
Disables menu from the start after title screen. You can call save screen through event but not menu screen.
In your Script Editor [F11] which is under Tools,
Right-click on Scene_Menu which is below Scene_Map and delete Scene_Menu.
For line 216 in Scene_Map, delete this- (to prevent error popup from pressing menu key)
For line 209 in Scene_Map, delete this- (to remove sound effect of pressing menu key)
Code:
$game_system.se_play($data_system.decision_se)
Please backup your project beforehand.