Is it possible to record a 4K time-lapse on iPhone?
No, the default camera app does not record time lapse in 4K unfortunately. I believe that there are third-party apps that will work. Alternatively you can just record a 4K video (set it to the lowest frame rate in settings) and then speed it up in iMovie on your phone. You might have to speed up>export>import>speed up a couple times to get it to be quick enough.