That is, sadly, not correct. There's a long thread (about 34+ pages) on the Apple forums about Mac Mini 2018 and Dell U4919DW not working properly at 5120x1440 - in MacOS. Restart the same machine into Bootcamp and Win10, and it works at full resolution. Lots of people have spoken to Apple (and Dell) and it's still not fixed over a year on - clearly the hardware can cope but the OS cannot. There's something about it being half of 5K (i.e. a height of 1440 rather than 2880) that upsets MacOS. People have tried a lot of things and end up either giving up, buying an external GPU or running two cables and using PBP/PIP - basically pretending it's two 27" monitors.
I'm sure I have suitable cables and adapters - I checked displayport.org for approved manufacturers and bought 8K capable cables and adapters where possible, DP1.4 where that was pertinent. The screen came with an HDMI cable which will be compatible (of course). I also used HDMI with the 2015 MBP I have (which I wasn't expecting to work) and tried both HDMI and DP with the MBP 2019. No dice.
The Dell was the first of the 32:9 ultra wide 5K 49" monitors - and if Apple haven't got that one working then there's probably no hope for the Samsung - LG might be different just because Apple have a close association with them.
There's stuff on the Dell forums too....
Dominic