Using a Mouse at the same time as being able to use the built-in Trackpad of a MacBook has worked in previous versions of macOS. But with macOS High Sierra, 10.13.0, they don't work in parallel anymore.
The issue exists both with all types of mice, including Bluetooth and USB, and third-party as well as Apple's original mice.
Is this a bug/issue or perhaps a new "feature", and can it be remedied?