aarch64 has a CPU mode, DIT (Data Independent Timing), specifically for allowing software to request all fancy value prediction stuff to be disabled for the duration of processing of sensitive data.

(doesn't help when the attack target is general-purpose/user-controlled code leaking things, but if you're relying on a process not leaking memory plainly available to it without full careful control of what the process runs, you've already been fully-SOL on that for decades and nothing has nor will nor can change about that)