Apple is one of the founders of ARM with very different licensing pricing and rights. Apple using ARM is very different from Google or Samsung using ARM.
Apple was involved in the founding of ARM, but their licensing isn't special. Many companies, including Samsung, have ARM architecture licenses which allow them to use the ARM instruction set with whatever custom design they want.
I don't think Apple has any ownership stake in ARM anymore, regardless of their initial investment in 1990. (Though I'm not sure how much they still had up through 2016 when SoftBank bought them)
Do we know that Apple has a special arrangement not available to other licensees?
Near as I can tell, in terms of licensing rights the only major difference is that they purchase an "architecture license" that gives them the right to create more custom designs, but this is a license available to and purchased by other companies like Qualcom, Intel, and others. And if Apple has lower royalty rates, it may simply be a product of their scale rather than special treatment.
But I don't know this for sure-- only that a little bit of searching didn't find anything obvious about special arrangements.
