Similarly I had issues regarding the missing 'Input' (aka User Input') option from my site builder toolbar to add a drop down menu, etc.
I noted many other users had the same problem, and their threads had not been resolved or closed before a resolution had been answered.
I can confirm to activate this option you must first select and activate 'Content Manager' within the '+' toolbar. And your done. The 'Input' option should now be available in the same menu.
Hope this resolves many headaches