Only once was there a noticeable breakage when a command like `git log` in the terminal would spit out all its output instead of displaying one screenful at a time. I'd expect someone following stable releases wouldn't experience any breakages.
I've been using emacs every day all day every time I'm front of a computer, since 1991. I need only one finger to count the pieces of software I've been using that long that have never crashed or broken on me in any way.
I have also run into compatibility issues when using older versions of Emacs with newer packages, and newer Emacs versions with older packages.
[1]: I totally did not build my blog on top of a bunch of these quirks. Every time one of them is fixed I'm reminded of the workflow xkcd. https://m.xkcd.com/1172/
But I agree that it is very stable and for me also doesn't break, even though I use use-package a lot and install many key packages. Maybe it is important to note, that I don't need everything there is out there and that I remove not well working packages quickly after trying them. From time to time I also look at my init file and get rid of no longer used stuff.