Cant Update from 12.4.7
Hi,
i have an Iphone 6s+ running on Version 12.4.7 and it didn't show the latest 13.5.1 Update as available. Reset the device and try on with iTunes was the same result "Your device is on the latests Version".
I would try to make a downgrade first, but didn't found the files.
Upgrade of an iPhone 6s on the same Mac works fine.
iPhone 6s Plus