i want to add button to return to main menu but when adding a button there is no option for it in the function area
After you add the button in UI go to Game Mind map(Menu Editor) and connect the button circle to the load circle in the main menu
you need a navigation button,then select "back jump" as function and then "Main Menu UI" as back to. OR you set function as "Default" and then connect the button in the mind map as @lqifqkt mentioned above