Not according to apple's own litreture I've just come across - incoming disappointment
Record ProRes videos with the iPhone camera to improve recording quality and enhance editing capabilities.
support.apple.com
Insanity, dedicated ProRes encoders/decoders on SoC and a 1TB storage option and no ability to record 4K60 unless using external storage - absolute nonsense from Apple there with yet another artificial imposed limitation, no doubt held back for the 16 Pro next year - tedious - "iPhone 16 Pro now features a 2TB capacity to record 4K60 directly to your iPhone without the need for external storage" - there's your marketing roadmap - suppose it's obvious
Even the argument of internal space not being sufficient ProRes 4K60 should come in at around 12GB/Minute so a 1TB should be able to record over an hour's worth of footage which is still plenty
I best make sure I carry a spare SSD out with me every time in the off-chance I may want to record in 4K60 ProRes, convenient!