Xbox One X - Resolution & Performance

Virtually all Xbox One games are compatible

It will not take advantage of the resolution and features of Series console. It will deliver Xbox One levels of performance on Series S, One X on Series X

I have no idea what Korhog is talking about. Killer Instinct is locked to 60 on Xbox One X. Changing the resolution will have no impact at all.

I'm a big PC player now, I too own an RTX 2080 with a i7 8700. Turning off VSync and lowering the resolution on a PC will provide more performance on PCs because as PC games have these options built into the games and the graphics hardware settings.

Consoles don't generally have these options unless the developer implements them. The Tomb Raider games have 'performance' modes on Xbox which puts the game into 1080P and therefore provides better performance.

But putting the Xbox One X into 1080P won't change anything. Regardless of these settings, if a game is 4K it will run in 4K and then downscale to fit the display resolution. Only on the PS4 Pro does changing the resolution in the settings have a direct
impact on performance, but this was by design.

Also note that these 4K claims on the Xbox One X are not quite all they seem. Sure, the Xbox One X can do 4K (or 3840x2160), but most games use a form of dynamic resolution scaling, temporal up-scaling or GPU checker-boarding to reach or give the appearance
of a full 4K resolution. This is done to reach or maintain a certain performance target by the developer, be that be 60 fps or 30 fps.

If you're interested more about these things, I suggest you look at the videos
https://www.youtube.com/user/DigitalFoundry make on YouTube.

Rainbow Six Siege Series X|S update lets you have performance mode and a resolution mode. The performance mode on the Series S only gives you a 1080p up to 120FPS. The resolution mode gives you 1728p at 60 FPS. The game does not show in 4K, hence why the graphics look pretty much the same as the Xbox One.

If you purchased the Xbox One X from the Microsoft store, you can talk to Xbox Support about returning the console (choose phone or chat): https://support.xbox.com/contact-us

The performance of how a game runs on the Xbox One X will depend on how well the developers optimize the game on Xbox hardware. There are plenty of games that run in 4K, but those games are limited to what is currently
found in the
Xbox One X Enhanced list. Games that are not "enhanced" will still gain subtle performance benefits, such as maxed resolution (if dynamic resolution is used), stabler frame rates, and a few other boosts - but in 1080p at best.

In the case of Fallout 4,
Bethesda made no claim that their game would run in 60FPS.

That would be up-to the developer of the game in question. The Xbox One and, in general videogame consoles, don't allow as much granular control of the graphical and performance options of the videogames as a PC does.

For example, with the Xbox One X Enhanced games, some give you two options on how to use the extra power of the Xbox One X. One would be "performance mode" in which the game might display in 1080p but have better framerates, or focus on the graphics,
meaning better resolution and textures, but the framerates aren't as stable.

Again, this depends on how the developers decided to include this options in their game.