"In the Designer section, the 'Connectivity' category in the Palette is not visible, and some other components are also missing from the Palette. How can this be fixed?"
Check your Project Properties, Set Blocks Toolkit to Default.
thank you very much. i was trying to fix it for about a week.
A post was split to a new topic: The results of the build of the App Inventor APK cannot be opened on the cellphone, only a white screen