The keyboard layout on Apple computers is special and some keys are missing. For example there is no Insert key to toggle between insert and overtype. LibreOffice supports the function and you can switch by clicking the respective panel on the status bar.
Figure 1: Status bar panel in Writer to switch between insert and overwrite.
But the question remains if we should introduce a shortcut for users who prefer not to grab the mouse (see ticket tdf#107918 on Bugzilla). The most common way is FN+Enter but some applications use less easy reachable combinations like Ctrl+Cmd+O to avoid accidentally key press. In any case the shortcut would be hard coded and not be customizable. What do you think (please enable Polldaddy)?
By the way, Microsoft Word on macOS provides an option in the preference dialog for this.