There is some kind of system error that various repair attempts using the (latest v. 4.5.2) Tweaking.com Windows Repair utility is, at least not yet, capable of diagnosing and fixing.
As of June 13, 2019 the current Windows 10 64-bit is: [Version 1903 Build 10.0.18362.175].
However, another machine [Version 1903 build 10.0.18362.86] cannot further update due to KB4503293 installation Error: 0x800f0988
A search for "Error: 0x800f0988" found nothing useful.
Note: have already tried using the various repair functions of the Windows Repair utility, such as booting to Safe Mode, running sfc /scannow, chkdsk /f, and the numerous other repair functions within the utility.
Thanks in advance.