This paragraph is highly enlightning to me. So Apple engineers the software for each chip separately? They first build the OS for M1, then M2, then M3? That's not going to scale well. Also the "software engineering management team" is searching for bugs themselves? No quality assurance team? That explains a lot... Also that fixing bugs is not part of development explains why Apple often doesn't fix bugs for years...
This sentence is confusing, but I don't think it means what you think it means, because this is not how software works. Operating systems and the software that runs on them, are compatible across the board with the processor they are paired with. Microsoft doesn't create separate versions of windows for each processor iteration out there and neither does Apple, aside from the random driver updates which is a component fix.
Also, if you read the whole sentence it says, "Apple last month finished the first "M1" versions of iOS 18, iPadOS 18, and macOS 15". The M1 is a desktop only processor, why would they also create software versions for iOS18 and iPadOS 18?