For the EU, the issue is that Apple intends to recoup this investment through premium-pricing a different product in another category - one that has many low-cost competitors.
Wouldn't this best be resolved by productising the Apple LLM? Earphone API becomes open, as required by EU. However, use of the Apple LLM would be controlled by license. Earbud competitors could either license Apple's LLM, perhaps on a FRAND basis, or they could install their own LLM on an iOS device. Apple may bundle its LLM but must allow users to uninstall Apple's LLM, to free up space for alternatives.
In short, this isn't and shouldn't be about access to IOS for earbuds. EU is right in this. It's about monetising access to the Apple LLM, for which Apple deserves a revenue stream.