The "only run approved software" part is a restriction imposed by Apple. It is not because of a physical limitation that makes them not real computers.
Technically there’s a real computer in my refrigerator, my printer, and my headphones but I don’t have any expectation that these are general purpose computers that are available for me to compute on. I think it’s those expectations that matter and it isn’t always black and white.
I look at my phone as being similar to a PS5. I understood that both devices were somewhat locked down when I bought and in fact that’s part of the reason I bought them. If the PS5 had an authorized mode that could run any software it would be a worse device. If I wanted something more open, those devices are available and that’s what I would have bought (and have bought in the past).
Yes, we get it, those computers are intentionally locked down by their manufacturers. That lockdown is what the problem is.
You can use this argument to justify anything companies want to lock down.
Apple does sell real computers under the Mac line.