Good points. This is a productivity app, but I'd like an answer to the original question, please: how many billions of dollars of revenue does the Mac generate for all developers across all categories of apps? Windows?
On both Windows and Mac, all big and many small app developers have their own billing and sales. When you buy Photoshop, MS Office, IntelliJ, or even many small tools, then you skip the app store, pay them directly, and download from them directly. So not even Apple or Microsoft know the numbers.
Microsoft can guess, at best, what kind of revenues there are for third-party software. They have no idea.
Apple, they can only speak authoritatively about their own App Stores, but they don't give out these numbers.
Linux, well... it's Linux. My guess would be that revenues are smaller for this platform, because hardly anyone charges for their stuff. Actually, I wish more paid work would be done for Linux. I'd be happy to pay for good apps.