My wife uses Arch (actually). She calls it the internet, when she really means Facebook. She knows it isn't Apple but it gets a bit vague after that!
The last time I had to fire up the Mesh Central client to sort something out on her desktop from work was around three months ago. Every couple of weeks I ssh into it, update it and schedule a reboot for 03:00.
If the client is blocking OS fingerprinting by returning generic navigator.appVersion and userAgent values you should probably just assume Linux in the first place.
Six months after I very proudly bought my framework diy, installed by usual arch linux and covered it in Unix stickers I was talking about repairability and sustainability and how cool my laptop was and my wife said she thought it was MacBook. She has been to Linux conferences, met Torvalds and games on a Linux desktop most weekends. People have a lot going on in their lives and everything doesn't resolve around computers for most of them.
If they thought about it most might figure out that their operating system isn't called Microsoft Office but their computer is a utility to write docs or consumer media and game. They don't need to constantly think about who made the hammer to use it.