Earlier quoted context omitted.
if I write a bit of software and target ARM64 and it cannot run on x86. Does that mean that x86 has a specific purpose now and is no longer a general purpose CPU?
That's not the same thing. An instruction set is an inherent aspect of a CPU; you can't have a CPU without one. Also, you can emulate or translate instruction sets between general-purpose CPUs, or in most cases just recompile the higher-level source code. The underlying logic will be executed regardless.
Sure, apple suck at sideloading, hopefully the EU ruling will make it a possibility, but then say that instead.