> After getting things working in Windows, I noticed that I can only pair 1
> controller at a time. Is it possible to have more than 1 controller paired?
Yes, it was possible last time I checked. A new "feature" of some (not
so) recent Windows 10 update maybe?
> If not, is this a platform-specific issue, i.e. would I be able to pair 2
> controllers if on macOS or Linux instead?
Some MacOS update years ago lead to a smaller number of controllers that
you could use in parallel (not sure why, it worked flawlessly in the
prior version). It was still greater than 2 if I am not mistaken.
I never had problems with multiple controller on Linux.