If someone were to write code to their software fixing bugs, how and why can that break other code/features if it’s not meant for that? A common example are Nvidia drivers “breaking” or Microsoft patching one feature but breaking many, many other features.
If code is meant to be hyper specific, how can it affect any other feature?
The different parts of software are (maybe) meant to be independent, encapsulated from each other, but in practice it’s hard to actually do that. So if you change the behavior of one part, the other parts that depend on it directly or indirectly often need to be changed as well, and certain types of issues are easy to miss, especially when you aren’t targeting a homogenous hardware platform like a game console.