why can’t I run 120hz at 1080p xbox series x on LG 34GL750

Hello friend, my name is Oskayra, and I will be happy to help you.

Beforehand, it is important that you keep in mind that this is a public community forum, so we are players like you, we are not employees of Microsoft or Xbox, so we do not have access to any user account or check anything from the forum. All users help each other with common problems.

Note: This is a public forum therefore, I suggest you not share your personal information.

I am very sorry for the problem you are going through, with the intention of being able to help you, I did an internal search in Xbox Support and I found a publication where they give the following recommendations regarding the resolution and I thought it was good information, which you should take into account:

Note: If you can't find your TV resolution, make sure TV Connection is set to Automatically detect.

Use the settings below as a guide to make adjustments.

Aspects that you should take into account:

Some of the settings below will not appear unless your TV or monitor supports them.

If you don't see the TV resolution, make sure TV Connection is set to Automatically detect.

The console will automatically switch to the previous settings if you do not confirm the new settings within 20 seconds.

Select 4K TV Details in Settings to see more information about your TV's capabilities.

Information Source (Credits): https://support.xbox.com/help/hardware-network/display-sound/change-tv-display-resolution

Pay attention to your answer, try the method to see if it works for you.

Sincerely,
Oskayra.

I have same issue but with my Acer Nitro VG271 144Hz. Xbox series X won’t run at 120Hz 1080p. That must be problem with xbox series x because works perfect with Asus RX480 8GB (144Hz 1080p HDMI2.0). I am very dissapointed. 60hz is a joke.

for 120hz you need i think hdmi2.1.

besides connecting the s at 120hz is not going to magically let it run at 120fps, you will be lucky to get 40fps on most games. kills my eyes running so slow.

HDMI 2.1 is only needed if you plan to game at 4K for 120hz , on a 4K 144hz monitor, However there's no gaming monitors available at the moment, that yet has HDMI 2.1, the first HDMI 2.1 monitors that are likely to come in are around the same time as the
Series X (Q4) launch or early 2021 (Q1),

1080p and some 1440p monitors can do 120hz over HDMI 1.4 if it's supported, but best ideally is HDMI 2.0 for 1440p for 120hz,

HDMI 2.0 can do 1080p / 1440p at 120hz and 4K at 60hz,

HDMI 2.1 can do 1080p / 1440p / 4K at 120hz.

For the Xbox Series X, it best to get a 4K TV or monitor that supports 120hz and has HDMI 2.1, to get the full potential out of the Series X.

Hi,

This is the same monitor as I have. I mainly use it for my PC, but I've also connected my Series S to it too. Unfortunately, you won't be able to select 1440P and 120Hz on the LG 27GN850 as it tops out at 100Hz on HDMI at 1440P.

The work around is to change the resolution to 1080P and then select 120Hz. Games on the Series X will still render at 4K but be super-sampled down to 1080P. Yes, it's not as good as the native resolution, but the loss in picture quality shouldn't be that
noticeable. I'm pretty impressed how my Series S looks on it.

Oh okay, but i can’t turn 120 fps on a low résolution ? I Know we must to have 2.1 hdmi for 4k120fps, and my motion rate is 120 , its not good ? , so i cant have any 120 fps mode ? , i dont understand wy Samsung Bride this .thank for your repons

Motion rate doesn't make your TV 120hz,

Your TV is a 60hz display with a 120hz motion rate, motion rate is more for watching movies or fast action sports from my understanding, making fast running/moving images look smoother and less blurry,

I also have a 4K Samsung TV, which is a 60hz display that has a 120hz motion rate,

It doesn't matter what resolution you choose 1080p / 4K, if it's a 60hz display, the most you'll get is 60 fps

The LG CX is the best TV for Series X at the moment or your going to be looking at a PC Gaming monitor where you can get 1080p 144hz / 1440p 144hz or 4K 144hz,

with 1080p and 1440p 144hz monitors you can get to play at 120hz which will get you to 120fps for games on Series X, 4K is more demanding and most games will be locked to 60 fps at 4K on Series X.