This is for macOS only, which should be reflected in the title. For those using Linux, I wanted to achieve the same thing a few years ago and ended up using Xep

This is for macOS only, which should be reflected in the title. For those using Linux, I wanted to achieve the same thing a few years ago and ended up using Xephyr, which is a nested X11 server that gives you another display (not the same thing as a virtual monitor). I remember having quite a hard time to get that setup working but I don't remember what made it difficult… The idea of a virtual monitor that continues yours on the left or right side of your screen like an actual external monitor is actually pretty neat, it offers a much more frictionless usage than an entirely separate display. I wonder if there an easy way to do this on Linux.