I'm sure everyone on this discussion board knows why this will never be the case, unfortunately.
With that said, are there any regularly-updated aftermarket ROMs that are privacy-focused? I've had a rough look at LineageOS[1] - a continuation of CyanogenMod - and it seems to mostly fit the bill.
I'm aware of CopperheadOS, but they had a "touch" of infighting about half a year ago[2] and mostly dissolved.
I too am moving away from Apple products, for the same reason. They are reaching expense levels (especially in my country) that I simply can't justify when I can get a HP or Lenovo business-grade laptop with drastically better hardware specifications and install simply OpenSUSE on it. Without going all-in on the Apple ecosystem to fully reap the rewards, it's simply not worth it for me to use any of them.
It's sad I will have to move back to Android within a year (I can neither buy big iPhones nor spend those amounts the way the new ones are priced). I wish there were fully functional privacy focussed ROMs that was shipped by Android OEMs.