Using hot keys is nice, but hot keys (intentionally) don’t work while my screen is locked. I contemplated mapping an xrandr call onto a smart button (Shelly Button 1, essentially triggering an HTTP request), but in the end grobi has the same effect and is even more convenient than having to press buttons.

For most situations you do not need to do anything difficult to plug any number of monitors to a Linux computer with a modern, full-featured distro, other than arranging them. Mac does a better job of remembering your setup and adapting to a monitor disappearing, but it's not that much better.

I'm still not sure I understand why the author needed this tool, may be because they have more than one computer plugged into the same monitor?

Debateable. But it sure started with huge step backwards. On X11 all relevant functions are at least standardized within the xrandr protocol. On Wayland you don't even have that. So it really depends on the compositor if it works or not where each is doing its own thing which is just crazy. I prefer the 70s standardization model of "mechanism, not policy".

mostly. With first releases of Win 10, it was more than challenging.

But one day a young engineer asked if I could hear my circuit when the load changed.

I could not. I have become what I hated. The cycle continues.