Why can't I duplicate a 30-minute 4K 60fps video on my new iPhone Pro 16 with ample storage?

I just recorded a workout routine of 30 minutes using my iphone, in 4k 60 fps, thats why i bought the new iphone, to record my own workouts. But now i can´t even DUPLICATE the video in the PHOTO APP, is starts but stops in the middle and i have to cancel it.

I dont use ICLOUD because i just have 5 GB and not enough space. Thats why i got the 252 GB Iphone. But the video is in my PHOTO APP.

So what´s the problem with this IPHONE?