Ultrawide issues

[Nipplenator]

Hi everyone,

I have an issue with my monitor. It is a LG 34um59-P - 21:9 ar, 2560x1080 .
Well, more like i created one.... let me explain:

I recently (and finally) got into the VR game, I got a Oculus Rift (the old one). While the oculus has its own issue (bent pin in the hdmi port, but it does work), multiple friends recommended me to use the hdmi connection on my GPU and do not use adapters, which i confirmed myself do not work.

So i wanted to connect the above mentioned monitor do a different port. Here's where my issues begin. I have a Vega64, so only 1 hdmi and 3 DP's. 
First i bought a DP to HDMI cable but that only displayed 1920x1080. Nothing else worked - I tinkered with the monitor settings, tried to set a custom resolution...
I read the whole "Guide to Display Cables / Adapters" pinned in this forum and i believed to purchase a adequate adapter. It was listed as DP 1.3 m and HDMI 2.0 f, supporting up to 4k60hz.
When i connect it, the screen starts to flicker, tho you can see it showing the full resolution for a second, it doesn't work in the end and just displays a blue screen.

Anyone here managed to get this monitor to work over DP?
Any help will be appreciated.