I had exactly one issue with a macOS upgrade - when they introduced APFS. The upgrade process has failed in the middle with an FS-related error, but AFAIR it resolved itself after rebooting and retrying. For comparison, Windows 10 and various popular Linux distributions have caused me a lot more after-update trouble: input devices ceasing to work, graphics drivers breaking and falling back to the built-in generic ones (with a 800x600 resolution, on Windows), graphics drivers breaking and not falling back to anything, but just causing X to fail to start (on Linux). Once (a few years back, I admit) upgrading Debian testing brought in a new version of the kernel that turned out to have some ACPI-related bug on my machine and consistently freeze about 30 - 60 seconds after booting. This all is of course just personal experience, but I think I'm not the only person with similar ones.