I've had the s21 ultra for a almost a week now.
It's an amazing phone in general BUT it gets super super hot whenever using the camera for more than a minute. This excessive heat causes the camera to stutter and lag and a zoom call of 5 minutes caused the phone to get so hot it just shut down! I've updated twice already including the latest firmware just yesterday but without any noticeable improvement. Reading other people here reporting the same is very very worrying as I was sure I just had a faulty unit. This is a wake up call to Samsung.
It is Exynos, and it is more than disappointing. My main reason to upgrade was the cameras(which are very impressive) , and it is currently unusable unfortunately.