Mac mini uses incorrect resolution.

It appears you have the display set to one of the HiDPI modes (3200x1800 instead of 3840x2160). When these modes are selected, the Mac's GPU's "internal" resolution is set to twice the actual delivered resolution, which it then scales to the delivered resolution. By doing this, scaling is much more natural and smoother since it is an integral scaling that if the internal was 3180x2160 and then scaled to the 3200x1800 which would result in poor image.

This is commonly done on all Apple Retina displays (Apple's term for HiDPI).

So what you see is what is to be expected. As example, if you select a mode to "look like" 2560x1440, the "internal" GPU resolution would be 5120x2880. If you chose the native resolution of the display, both would be identical. In the case of a 4K display, the entries would both show 3840x2160.

I use my 4K display at native resolution, which gives:

LG ULTRAFINE:

  Resolution: 3840 x 2160 (2160p/4K UHD 1 - Ultra High Definition)

  UI Looks like: 3840 x 2160 @ 60.00Hz

When I switch to "looks like" 3008x1692:

LG ULTRAFINE:

  Resolution: 6016 x 3384

  UI Looks like: 3008 x 1692 @ 60.00Hz

So, what you see is the way it is supposed to work!

The display may support up to 6400 x 3600 on a PC with DisplayPort, but Apple's HDMI port delivers 4K 3840x2160 @ 60Hz. Makes no difference in the HDMI 2.0/2.0b/2.1 cable that you use.

That is strange, perhaps it is the cable that is confusing macOS.

https://www.usa.philips.com/c-p/BDM4350UC_27/brilliance-4k-ultra-hd-lcd-display

If you are have trouble finding the optimal resolution for that display?

Go to Apple > System Preferences > Displays > Display tab > hold the Alt (option) key > click on the Scaled button.

https://support.apple.com/en-us/HT201177

If that does not help?

You can also get and test a USB-C to DisplayPort cable between the 2018 Mac Mini and that display.

usb-c to displayport cable

FWIW I'm running dual older 21.5" Samsung Displays on my 2018 Mac Mini and they are reported correctly.

Intel UHD Graphics 630:

Chipset Model: Intel UHD Graphics 630

Type: GPU

Bus: Built-In

VRAM (Dynamic, Max): 1536 MB

Vendor: Intel

Device ID: 0x3e9b

Revision ID: 0x0000

Metal: Supported, feature set macOS GPUFamily2 v1

Displays:

S22B310:

Resolution: 1920 x 1080 (1080p FHD - Full High Definition)

UI Looks like: 1920 x 1080 @ 60 Hz

Framebuffer Depth: 30-Bit Color (ARGB2101010)

Display Serial Number: H4LC600604  

Main Display: Yes

Mirror: Off

Online: Yes

Rotation: Supported

Automatically Adjust Brightness: No

Connection Type: DVI or HDMI

Adapter Firmware Version: 8.63

S22B310:

Resolution: 1920 x 1080 (1080p FHD - Full High Definition)

UI Looks like: 1920 x 1080 @ 60 Hz

Framebuffer Depth: 30-Bit Color (ARGB2101010)

Display Serial Number: H4LC504459  

Mirror: Off

Online: Yes

Rotation: Supported

Adapter Type: DVI or HDMI

Automatically Adjust Brightness: No

Adapter Firmware Version: 2.19