All of the things you mentioned are annoying level problems.
ATMs
Card payment should still work, ATMs are more of a footnote in today’s world. I can’t even remember the last time I used one. If I were to use one and it didn’t worked it would be annoying.
There is a lot of industrial machinery running Windows 98 or XP to this day.
And there are lots that don’t. Plus, wine has excellent support for old windows versions, I would be very surprised if something didn’t just worked. So there would be some downtime while people annoyingly set things up with wine.
A lot of POS devices too.
And a lot of POS don’t, the ones that do would have to change OS, an annoyance.
Almost all accounting is done on Windows.
The ones that don’t would receive lots of new clients, and the rest would leave clients annoyed while adapting.
The amount of chaos if it disappeared would be immense
I think you’re probably exaggerating the proportions, nearly 100% of the hardware that runs Windows runs Linux. Yes, there would be some chaos until things migrate, but there are alternatives that are reachable and usable.
Linux is probably still worse because it would mean that more than half of smartphones are suddenly bricked,
That’s an annoyance. It’s not just some phones, it’s absolutely every network connected device that is not a Windows or apple thing. If you Google something on your phone yo go through possibly 20 different Linux devices back and forth.
literally all of the internet just stops working
This is the big one, removing Linux menas breaking the internet (and most intranets). And it’s not breaking one thing or another, it’s breaking every single internet service, the ATMs in your windows example wouldn’t work, nor would any PoS, since they usually depend on inventory management and card connectivity.
And it’s not a “until people reinstall their system” deal, it’s breaking in an essentially unrepairable way. There’s a very high chance that outside of a very small subset of devices there’s just no alternative to Linux. That’s the difference, Windows disappearing is a hiccup while things adapt, Linux disappearing is chaos without a foreseeable solution, 90% of electronics become e-waste.