Apple literally designed large parts of AArch64. There's no do wtf you want license that you can go out and buy, but Apple has one none the less from the sheer fact that it's partially their's to begin with and they negotiated it with ARM before AArch64 was even a twinkle in their eyes.

ARM probably has some trademark mechanisms that they could in some world use to enforce compliance from Apple, but Apple has been super duper careful to refer to it as Apple Silicon rather than ARM.