Windows 10 upgrades
If you're running Version 1809 or older and Windows Update isn't offering the upgrade, it's nearly certain that a safeguard hold blocks 1903 Upgrade on the target PC. Here is more info.
Despite a May 6 claim of more-or-less general availability, so-called May 2019 Update general availability still leaves PCs out of the automatic upgrade proffer that clicking "Check for updates" is ...
After waiting 10 days in vain for WU to offer, Production PC gets 1903 upgrade when I manually resort to the Update Assistant instead. Spoiler alert: the upgrade has a happy ending!