I mean, among "younger" American HNers (those who went to middle or HS in the mid 2000s to mid 2010s), MacOS X Leopard or Windows 7 was probably a much more foundational desktop OS - most of our school computer labs used one or the other, as did our families.

I could make a similar argument for Win7 and the indie gaming scene.

Nah, Windows 7 RTM was ~a month before most school years started back up in 2009 so relatively few schools even considered starting to roll it out until at least 2010 (usually upgrades are done by then, not just beginning). E.g. I was class of 2012 and it wasn't until my senior year the rollout started (it was about less than half complete that year). Meanwhile they had us doing Microsoft Office classes twice a week on XP since 2003.

Can't say for Macs, the district hadn't used those since the iMac G3. After I graduated it was only a couple of years (maybe 2015?) before they rolled out Chromebooks, so 7 didn't even have much staying power.

Shoutout to kipix studio deluxe.

No way. I'm in that group, and not only did every school computer lab I encountered run Windows, everyone I knew had Windows at home. Macs simply are not as common as you're thinking.