“We’re not sure if this will work or not, and we don’t want to deal with you if it doesn’t, so we’re not even going to let you try.”

This is Apple. They don't expect their users to know what a User-Agent is (and even less how to install a User-Agent switcher extension).

To be fair, Safari has a user-agent switcher built-in. Just enable the developer tools.

Not all Apple users are clueless.

It’s called Developer Tools and not User Tools for a reason

What do you think Firefox calls it?

The same, for the same reason

Isn't it just a name?

A user can easily enable the developer tools if needed, same way I'm not a mechanic but can open the hood of my car.

You can open the hood of your car, but there’s probably not much you can do there.

Of course I can. Add cleaning water, check oil levels, replace a light bulb. No much else I can do, but others may, and other won't even do any of this.

Point is, this is not a binary choice. Between user and developer there are many people with varying skills that will use a user-agent switcher if needed.

It’s not about capability, it’s about interest.

Most people could do a bit under the hood of a car, but they simply don’t care.

It’s the same thing with computers. Most users are savvy. They just don’t care.

In my experience (systems engineer/devops for both Windows and Linux for more than 25 years), very few users are actually savvy. Even those working in tech.

Our definition of savvy probably differs.

That is possible. Mine would be more or less "someone who knows what they're doing"

Yep, and this philosophy has been a significant factor in Apple's widespread success

Extremely frustrating. If a user is smart enough to use Firefox, they're probably also smart enough to open another browser if a site does not happen to work on Firefox. (Which I haven't experienced for a while, except when using ESPHome which requires WebSerial)