Per-display scaling works in X11. I happen to use a single DPI setting that's an in-between for both monitors, but that's not a requirement, you can scale per-monitor if you prefer that. Wayland will handle this a bit better, but even in X11 you have options.
I agree that "just use Linux" isn't an answer to privacy concerns in the mainstream, if for no other reason than that the current conversation about Apple is a conversation about phones, a platform where Linux is not currently usable. Purism/Pine phones are exciting, but they're not usable smartphone alternatives yet. Really if we want to talk about Apple's recent changes, I'm not sure any desktop OS is relevant to that conversation.
My frustration here is that a lot of the people who use "year of the Linux desktop" seem to have a really outdated view of what Linux is actually like as a daily driver. HDPI scaling was a huge problem on Linux for a long time. It's a lot better now.
The main barriers for Linux adoption at this point aren't technical. The barriers aren't trying to handle multiple displays, or projectors, or wifi cards, or even getting hardware -- there are multiple companies now that sell good preloaded Linux laptops. That doesn't mean the market share is magically there or that we're going to see a mass migration to Linux any time soon, but the market share is good enough that Linux gets decent support, and stable enough that Linux gives me generally fewer problems than Windows used to (that may have more to do with the quality of Windows degrading though). For a long time that wasn't the case; even until a couple of years ago I would have said that Linux was way behind the curve on touch/tablet support. That gap is pretty much gone now as far as I can see.
That part of the meme that's related to grishka's "sure Linux is a workable desktop, just don't hook any monitors up to it" comment -- that part is dead as far as I'm concerned.