The first is that the RovingTabIndexProvider now takes an optional options prop for tailoring the behaviour of the library. If you have previously used the direction prop on the provider then you will need to update your usage as follows:

// Old:
const SomeComponent = () => (
  <RovingTabIndexProvider direction="vertical">
    {/* whatever */}
  </RovingTabIndexProvider>
);

// New:
const SomeComponent = () => (
  <RovingTabIndexProvider options={{ direction: "vertical" }}>
    {/* whatever */}
  </RovingTabIndexProvider>
);

Note that it is fine to create a new options object on every render - the library's internal state is only updated if the individual values of the options object's properties change.

The second breaking change is that now, when an element that is part of the roving tabindex is clicked, focus() is no longer automatically invoked on the element. The previous behaviour of this library was that focus() would be invoked on a click. The reason for this was that browsers are quite inconsistent in their behaviour when a button is clicked, and invoking focus() in that situation improved consistency. However, @kripod suggested that a better default is to not automatically invoke focus() on click. If you want to maintain the old behaviour then you can use the new focusOnClick option and set it to true:

const SomeComponent = () => (
  <RovingTabIndexProvider options={{ focusOnClick: true }}>
    {/* whatever */}
  </RovingTabIndexProvider>
);

There is also a third option available on the RovingTabIndexProvider, called loopAround. If set to true then tabbing wraps around if you reach the very start or very end of the roving tabindex items, rather than stopping. This option does not apply if the roving tabindex is being used with a grid.