There is a serious security flaw in billions of Intel CPUs that can let attackers steal confidential data like passwords and encryption keys. Firmware updates can fix it, but at a potential significant performance loss.
Even on a single user machine, multiple users are very much a thing. Even Apple has left behind the DOS-like architecture where everything runs with the same rights. All current systems run with multiple concurrent users, notably root (or the Windows equivalent) and the keyboard operator (as well as dedicated ones for the various services, although that’s maybe more a thing in Unix/Linux than Windows).
Even on a single user machine, multiple users are very much a thing. Even Apple has left behind the DOS-like architecture where everything runs with the same rights. All current systems run with multiple concurrent users, notably root (or the Windows equivalent) and the keyboard operator (as well as dedicated ones for the various services, although that’s maybe more a thing in Unix/Linux than Windows).