Technically yes but just because they have a scheduled major release every 6 months doesn’t mean you’re going to see significant breaking changes. They’re not as conservative as Ember in that regard (still on 3.x!) but relative to React, Vue, etc things aren’t changing as quickly.

That's never been my experience at all. React's backwards compatibility has been always in a class of its own.

Angular? Migrating from one major to another was always source of great pain.