Not getting 5120 x 2160...need help

Imagine wrote:

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Ok, so I was able to switch the DisplayPort 1.4 to 1.2, and I'm able to switch it to 5120 x 2160, ...

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Display Stream compression means the display has to have enough really fast compute-power to do the de-compression. If the display does not have enough, it may limit top resolutions under DisplayPort 1.4. Then, counter-intuitively, DisplayPort 1.2 can give higher resolutions.

Try using the free version (it has in-app purchases) Display Menu app from the App store to see if you can get the native resolution of the Monitor.

Also, what macOS version are you running? I would go to the latest, 12.3.1 if not already there since some users have had problems with monitor resolution with earlier versions.

When you select "Scaled" resolutions, your display will run at its MAXIMUM possible native resolution. The display should be excellent, and the text [and ONLY the text] has been scaled up to be readable, with lovely edges without stair-stepping along the diagonals of letters.

The issue is that when you go to look at what resolution it says, It LIES to you. You can no longer use the numbers it is telling you for comparison with other display or other settings.

To get accurate information, IGNORE what is says In Display preferences and use:

 menu >about this Mac > (system report) > Graphics & Displays ...

You will see two different resolutions. The one labeled Resolution is the actual resolution your displays set to without any fiddling around. The one labeled User Interface Looks Like is what resolution you would have to be running to get comparable- looking letters. In other word, not comparable to anything.

Sometimes you need to have a "talk" with the display (using On-Screen display settings) about its settings, which it then reports to the Mac as its capabilities, limiting the resolutions possible.

DisplayPort 1.2 Vs DisplayPort 1.4 (both embedded in ThunderBolt) may be the issue. The latter allows for Display Stream Compression, (DSC) which raises the effective data rate.

Imagine wrote:

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... except everything is tiny. Is there anyway around that?

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Yes, that is what SCALED resolutions in the Mac are used for. The display is set for highest resolution, and graphics are displayed at that resolution. Text (and only TEXT) will be doubled in size (or 1.2x or 1.5x, or 1.8x you get the idea). this improves readability, BUT: the reported resolutions under Scaled are all "looks like" resolutions, and are not comparable to ACTUAL resolutions.