Ternus is the leading candidate; VP of Hardware Engineering. He was very likely more directly responsible than Cook for all the things you liked about Cook's Apple.
My fear for Apple right now is how most decisions they make appear to incentivize them toward becoming a perpetual middle-man in all aspects of your interactions with their products. They don't manufacture much of anything anymore; its on-contract. They design the M-Series chips, but don't make them. Their software sucks; they'd rather just take 30% of your interaction with actually-good software. Their AI and search sucks; they just pay Google $30B a year for theirs. Etc and etc.