I wanted to know if it was possible to disable or hide some menus in my ArcGIS Online account for the public. I want to hide the Sign In menu, My Map, Scene, Group
Is it possible ???
No it isn't possible to remove the menu options.
What do you want to do?
If your goal is to prevent access to your site to the public, you can disable anonymous access via the Organization > Setting > Security
If you want to more explicitly control content for the public, consider creating an Open Data site.
Hope this helps,