LG Monitor 43" Monitor... The right connection

Internally, they are the same. The protocol inside USB-C display and ThunderBolt-3 display is exactly DisplayPort.

Once advantage of USB-C is that sometimes the display has enough extra power that it can change your MacBook Pro while it is running. But for the 16-in MacBook Pro, they generally do not provide enough power, so you need the Power Adapter instead.

The real differentiation happens ABOVE the nominal 4K your display will show. Apple sells a cable rated for 5K, for example.

Punchline: that high-end cable will work, but is not required for this setup..

Unchecking HDR will reduce the data rate, and therefore the heat generated.

The hardware is perfectly capable of displaying both in HDR. It is not as if it will slow down or anything based on the additional bits-per-pixel. But it is a faster data stream, and it likely will produce a little more heat.

A common complaint (if you do not take other steps to reduce heat) of this computer is that with too much data displayed on too many too-large displays, the computer heats up, and the fans spin up to reduce the heat. Some find that noise annoying, but it NOT a defect. When you ask your computer to work hard, it does.

Suggested strategies to reduce heat include Not running third-party anti-Virus, not running third party file-sync apps except on demand, and using a third party app to disable Turbo Boost.