As I understood it, Microsoft changed the way how Windows 10 automatically installs feature updates starting from version 1903. E.g., on this official Microsoft blog post it says:
Beginning with the Windows 10 May 2019 Update, users will be more in control of initiating the feature OS update.
This new “download and install” option will also be available for our most popular versions of Windows 10, versions 1803 and 1809, by late May.
But yesterday my private Windows 10 Pro x64 version 1809 automatically downloaded and installed feature update 1903 (and even did that while I was playing a game...). As far as I understand it, that shouldn't have happened. 1809 Home and Pro is still supported until May 12, 2020 so the case that it "soon reaches end of service" that is mentioned in the blog post should also not apply.
I did not change any hidden Windows update settings (like with a group policy or in the registry). Previously, I had it configured to be in the "semi annual" update channel (not the "targeted" one) so that I get the updates later, but even that option was removed from the GUI in some update (I assume because it "should" now be manual to install feature updates).
I did see that new "download and install" UI element on the Windows Update screen before it automatically updated yesterday. But of course I never clicked it.
Does anyone have an idea why my PC automatically installed the 1903 update?