Comment by lmm
> It's pretty easy to install a keyboard layout that supports it
Only if you don't need anything else from your keyboard layout. I use Dvorak and need to type Japanese, and I think either of those makes it impossible to enter macrons on Windows.
You can have multiple keyboard layouts installed, and it takes a fraction of a second to switch with a shortcut key (on Windows it's Win-space). I have a Māori keyboard layout installed on my work computer, but I only switch into it to type words with macrons, then switch back (I use ` more often and don't like having to double-press it).