Does anyone know any good sources for where I could find this information? All of the sources I've looked at have been unreliable, I've listed two of them down below who both also admit to being unreliable.

Unreliable sources:

1. https://www.statista.com/statistics/944559/worldwide-macos-version-market-share/ states

Note that the source has indicated the fact that Apple has been reporting Big Sur 11 as Catalina 10.15, making its reported market share incorrectly high.

2. https://gs.statcounter.com/macos-version-market-share/desktop/worldwide

Apple are incorrectly reporting Big Sur 11 as Catalin 10.15. You can read more about it [here](https://bugs.webkit.org/show_bug.cgi?id=216593).

Seems like no one really knows what the actual numbers are?