It does not mean that something happened with MacOS / OS X. If it stays the same and everyone else gets bigger, then the same gets smaller relatively speaking. Look at the dip for OS X in Nov 2023. Looks like almost the same amount of up for Windows. Also Chrome OS went a bit down and Unknown went up, only Linux stays the same.
So either something in their software changed or it was really a phase of people buying new computers and changing their OS. For a fact, I also build my PC in Nov 2023 (but stayed on Linux). Maybe that was a time of new hardware or lower prices, don’t remember exactly.