Q: iPhone App-Sync with iTunes issue

Today I downloaded a new iPhone App into

iTunes [12.4.3.1]

on a Macbook Pro [10.11.6]

which has several previously acquired iPhone Apps, all updated and all previously working on my iPhone 5 [9.3.5] (Firmware 10.01.00).

Recently, via USB, attempts at Sync-ing my iPhone work, however, the iPhone Settings/ Apps window within iTunes is entirely greyed-out, including the 'ticked check box for installing new apps' just below the list of Apps.

Today's new download is sitting there in the list with it's button reading 'Install", and, along with everything else, is un-clickable.

After reading an iPhone full restoration worked for others, I restored the iPhone with iTunes by selecting the listed option using my "iPhone Name".

Now all of the Apps are missing from the iPhone and are not able to be loaded as they all still remain greyed-out in iTunes under the iPhone Settings/ (Summary, Apps, Music/ etc).

However, as it was previously, I am still able to manually select within Music and Books and Photos, etc, and have such accurately Sync-ed with the iPhone presently.

How is it an updated iTunes and OSX are incompatible for Sync-ing updated iPhone Apps to an updated iPhone via USB?

Please help.  Thank you.