connecting 5k display to mac mini 2018 via DisplayPort

This is not possible due to the way Thunderbolt works.

Thunderbolt is merely a 'container' for PCI and Displayport signals, in the case of Thunderbolt3 it also contains USB3.1. So the Displayport signals come from the Mac (video chip) and are passed unaltered over the Thunderbolt cable.

The nearest thing to what you are looking for would be a hypothetical Displayport 1.2 to Displayport 1.4 adapter and these do not and will not exist. A diagram always helps.

Displayport 1.2 (from video chip) --> Thunderbolt3 --> monitor (still Displayport and still version 1.2)

A different adapter e.g. HDMI 2.0 would involve the following

Displayport 1.2 (from video chip) --> Thunderbolt3 --> Displayport 1.2 to HDMI 2.0 adapter --> monitor

The big problem is that Displayport 1.2 does not have enough bandwidth for 5K over a SST connection. Since the source remains Displayport 1.2 it will be sent too s_l_o_w_l_y to support drawing a 5K screen via SST at 60Hz even if hypothetically converted to Displayport 1.4.

I suppose hypothetically a Displayport 1.2 MST 5K signal (i.e. a pair of Displayport signals sent as MST) could be converted to a single Displayport 1.4 SST stream. Such a beast does not exist and the amount of processing may slow things down too much even if one was made. (Ignoring the cost issues.)

I would interpret dual-link SST as to mean MST.

The other possibility is that in order to connect say the Dell UP2715K to a Mac you had to use a special cable which used two Displayport cables and merged them together. Each Displayport half is a Displayport 1.2 connection providing half the 5K screen input. See the Dual Link displays section of - Using 4K displays, 5K displays, and Ultra HD TVs with your Mac - Apple Support

The LG display is not what Apple term a Dual Link display, it uses a single USB-C connection i.e. Thunderbolt3.

As such whilst the Dell UP2715K can be used on older iMacs and Mac Pros the LG Ultrafine 5K cannot. (They only have Thunderbolt2.)

Welcome to the Apple Support Communities!

I understand you would like to know what connections are supported with the new Mac mini. Take a look at the tech specs below:
Mac mini 2018 tech specs

Video Support

Support for the following combination of maximum concurrent display setups:

• Up to three displays:
• Two displays with 4096-by-2304 resolution at 60Hz connected via Thunderbolt 3 plus one display with 4096-by-2160 resolution at 60Hz connected via HDMI 2.0
• or
• Up to two displays:
• One display with 5120-by-2880 resolution at 60Hz connected via Thunderbolt 3 plus one display with 4096-by-2160 resolution at 60Hz connected via HDMI 2.0

Thunderbolt 3 digital video output supports

• Native DisplayPort output over USB-C
• Thunderbolt 2, DVI, and VGA output supported using adapters (sold separately)

HDMI 2.0 display video output

• Support for up to one display with 4096-by-2160 resolution at 60Hz
• DVI output using HDMI to DVI Adapter (sold separately)

Indeed Apple have not detailed anywhere I can find the version of Displayport available in the new Mac mini 2018. They have also not updated their 4K/5K knowledgebase article. 😕

The nearest 'answer' I can find is this article discussing the MacBook Pro 2018. See - https://www.macrumors.com/2018/07/20/2018-macbook-pro-titan-ridge-displayport/

From this we can see that two things are required.

1. The Mac needs the new Titan Ridge Thunderbolt3 controller chip
2. The Mac needs a suitable GPU and it appears the integrated Intel GPU is unlikely to be one

Therefore even if the Mac mini has a Titan Ridge controller it does not look like it will support Displayport 1.4. 😟

The Mac mini 2018 uses an Integrated Intel HD Graphics 630 chip. According to this - https://www.intel.co.uk/content/www/uk/en/support/products/98909/graphics-driver s/graphics-for-7th-generation-intel-proc… it supports Displayport 1.2 and eDP 1.4. eDP is for embedded displays and hence not applicable to the Mac mini. This would tend to confirm it cannot do Displayport 1.4