This all ended with Microsoft throwing its hands in the air and asking that I reinstall that year's Windows Creators Update, which—lo and behold—did the trick
This has been a constant problem with Windows 10 since the very beginning:
-- Clean install.
-- Programs A and B work just fine, but Program C won't install, or, installs but won't run properly.
-- Wipe and clean install again.
-- Program C now installs and runs just fine, but Program D won't install, or, installs but won't run properly.
-- Lather, Rinse, Repeat ..... until finally after 4 or 5 attempts everything is running (sort of) smoothly.
Another reason why I still run Windows 7 on my main computer.
The error code in question . . . . ."0x80070003," failed to narrow down any source for the error
It is beyond absurd that Microsoft still refuses to provide clear error messages that actually explain what is wrong.