Backwards compatibility on macOS is quite good. Whenever Apple breaks compatibility, they give a lot of notice, mark the functions in the headers as deprecated,

Backwards compatibility on macOS is quite good. Whenever Apple breaks compatibility, they give a lot of notice, mark the functions in the headers as deprecated, then wait a fair amount of time before actually removing them. For apps that are continuously maintained, it’s not too huge of a burden to keep up with most of the time. For apps that are no longer in development, it can suck, for sure, to not be able to use an app after a breaking change, though.