FCP is not fully compatible with "Cinematic" iPhone footage yet. The latest version of iMovie already is. I have friends who have the 13 Pro and iMovie, and it's pretty cool what you can do with Cinematic Mode in iMovie. So, look out for the next update of FCP.
I was going to buy the 13 Pro. But since I have seen quite some footage from friends who already have it, I'm hesitating. The bokeh or DOF on the 13 looks very artificial and sometimes simply ugly. Especially with hair or any outlines that are not clearly separated from the background. I may be biased since I recently bought a Canon R5 with high-end glass that produces amazing natural DOF, no matter what the subject or background looks like. And I know you shouldn't really compare some AI-generated bokeh on a phone with a professional camera and top notch lenses. But still, the difference is way too big if you only consider the 13 for this feature. OTOH, in-camera image stabilizing on the 13 is really good.
Thanks very much Ronny. If the Cinematic video is put on an older iPhone with iOS 15, I wonder if it has controls in Photos. If the DOF is change in iMovie, does this pass on to FCP? I would love to get a clip or two to see what it looks like.