This happened to me on two different Windows 10 PCs within 48 hours. I suspect it might be related to the fact that Microsoft stated Windows 10 support will end on October 15th, so upgrades are being forced.
On the first PC (an older gaming computer), I’d previously tried 11, discovered that NVIDIA had no intention of providing a compatible driver for my 1070 graphics card, and that the generic Microsoft driver it installed wouldn’t work with most of my games; they all shut down at their startup screens. So I rolled back to 10 and always refused the gazillion offers to install 11. The good news is that there’s now an appropriate graphics driver for me. But—as is usual with unnecessary upgrades—launching apps (so far, anyway) is now painfully slow.
On the second machine (high-end MSI laptop), it automatically installed when I simply turned the PC on. It seems to work, but again I did not authorize it nor was there an option to abort the install.
Windows (and Mac) system software upgrades seldom offer new features I find useful, invariably slow the machines down, require learning a changed interface and command set (for no apparent reason), and introduce software incompatibilities that may require expensive upgrades or render programs unusable. Rather than enhancing virtually anything that’s valuable to me, they lessen productivity and—in the worst case—require expensive upgrades or abandoning a previously functional PC. I’ll keep 11 for now, but I’m not happy with major system software updates occurring without my express permission.