How is it a prison? I use MacOS without an Apple account, block all call-home requests, install whatever I want. What would be a comparable hardware (ARM arch) and OS to replace it? That doesn't feel cheap and just works?

The problem of a prison often is not, that it is insecure. The problem is rather that you do not get out and therefore have a lack of freedom. MacOS lacks the freedom to tweak the system. Since it is all closed source a user has no other opportunity, but to trust apple in making it private and secure. When you are not ok, with a decision of some settings, the look of the desktop or whatever, one has no real solution to change this. With the use of software I just really do not know. Maby as you say, one can also install software from Github to mac without problem. I assume you know this better than I know. But in the essence. I think it is the lack of changing the system however you want to, since the code is not open to look at it, to change it, to compile it and distribute it to other people.