This is truer than you might imagine.
I recently had to explain to a 16-year-old intern that their phone is a computer. And that "apps" are recipes for that "computer". And that humans made all those recipes sitting on the phone.
This was clearly a quite shocking revelation. It wasn't a hard conceptual leap, but the "app abstraction" is so total that it completely cognitively blocked the idea that their desktop computer and their phone are effectively the exact same thing.
Of course, at that point, the obvious questions started: "So, I could run <desktop program> on my phone? Why can't I do <deskptop action> on my phone?" etc. Eventually heading to the inevitable "Why do the phone manufacturers prevent you from doing something you want to do that the phone is perfectly capable of?"
I don't think this is a fair statement. Image file formats are something that very few people need to think about these days. As another commenter pointed out, why wouldn't changing the extension trigger the OS to convert the file? It was worth a try.
Not everyone needs to be an expert in everything.
If you change the extension on any operating system and then open it in the image viewer, it does appear to work. It doesn't as image viewers do not trust the file extension and ignore it, but there is no indication of that to the average user.
Not all of them; for instance, if I rename a .jpg to a .png exension and try to open it with Gnome's EOG, it presents an error saying "Not a PNG file", instead of showing the image.
Apps are becoming so streamlined and gesture intuitive that children and young adults might actually be regressing in their tech competence while increasing their reliance on it. This is akin to cars packed with electronics, easing use while decreasing DIY repairs and understanding. This decreases our right to repair as a consequence of ease.
Many children will not navigate the antiquated forums and php sites that taught me problem-solving and a degree of independence. I'm not sure what will replace this lost experience for them.
I guess I joined the tech admin / helpdesk fields as a way of putting my money where my mouth is, like buying calls on these services' growing necessity.