You would not believe it. I found the culprit and it's ridiculous. The reason the 1809 to 1903 update threw the message in the OP... A thumb drive I had plugged in with a Linux Mint iso extracted on it I came home from work, tried the update again.. Same program opened and same error.. Then I had an epiphany. The ONLY thing left on this PC I haven't removed or disabled is this stupid 8GB thumb drive with a Linux Mint live install on it.. Unplugged it, re-ran the Windows update.. Boom... ZERO issues, flaweless install, it didn't even open the program that showed the error this time. I nearly had 7 strokes when this happened. A 7 year old 8GB thumb drive prevented an update from installing. Unbelievable.