I had problems updating a copy of Win10 1909, where after the restart or reboot it would get so far, then after one or more restarts just roll back to v. 1909. When Windows started up afterward it showed a message with an error code. That code was useless in my case, but Google the code if you have one and maybe it'll mean something. Windows Update History might also show an error code. Beyond that there are quite a few resources online with different tips and info about finding & reading the logs, though that might or might not be a fool's errand. I got lucky when the Win10 2004 setup routine finally threw me a couple of BSoD screens listing the file's name that was causing problems. From what I've read, I'm not the only one. Otherwise I'm not sure the problem could have ever been diagnosed. The logs etc. all were meaningless, showing everything was good until setup crashed, which wasn't logged, because it crashed, and there wasn't enough detail to say it was doing this exact operation immediately before it failed.
In my case it was not a file for an app that many others would have had installed, & any problems probably have to effect a huge number of people before Microsoft *maybe* notices. They missed the incompatibilities with Lenovo devices, & Lenovo sells a ton, while most every other problem that's come to light was reported by Insiders, often last year. Waiting for Microsoft to come up with a fix does make sense -- I'm just completely unsure it'll do any good.
Microsoft's settled on the name it's going to use for Windows 10 versions -- Win10 2004 is 20H1, for year 2020 1st half, with 20H2 just starting to be released to Insiders on the Slow Ring, which is now the Beta Channel, and the 1st build of 21H1 was just released to the Fast Ring, which is now the Dev Channel. 20H2 should be released sometime in the fall as a cumulative update to 20H1, with 21H1, which will be a full version install, coming sometime in the spring. Microsoft now lets you skip Win10 version upgrades/updates until your current version gets close to the end of support, when they'll start trying to force it on you, e.g. Microsoft is starting to push the 20H1 update on anyone running Windows 10 1809.
If you're looking for a bright spot, the closest I can come is that Microsoft released a fix for people having printer problems after the last round of fixes earlier this month. Unfortunately it won't come via Windows Update -- you have to download & install manually.
neowin[.]net/news/microsoft-finally-fixes-print-spooler-issue-for-the-windows-10-may-2020-update
