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.
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.
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?