I bought this cable:
I planned to use the DP++ function, but now Im not even sure if my Vega56 can output analog signals.
Im getting only low resolutions with max. 75Hz. The custom resolution utility didn´t worked either.
Does my card support DP++ analog mode?
Have I the wrong cable? Maybe this: https://www.amazon.com/DisplayPort-FOINNEX-Supports-Transmission-Desktops/dp/B01GJK0OY6
My monitor: IIyama Vision Master Pro 510
Display Port is entirely a digital standard with zero support for analog. That means VGA is not supported by any Display Port output or input on any type of device. Because of that DP++ only has provisions for converting to other digital standards, HDMI or DVI for example.
The cables you linked to are active adapters. They take in the digital signal from your video card and convert it to an analog signal. If you're having trouble getting a specific resolution or refresh rate that is most likely a limitation of the cable. You'll need to contact the cable's manufacturer to find out if their product supports specific resolutions/refresh rates.
i doubt that your Vega has a "analog-output-chip" - you need an active adapter for that!
Try other option: from your Vega HDMI to your Monitor, with HDMI to VGA adapter. So you can review iF the monitor supports or codec the digital signal from your Vega. I've noticed in some videos your adapter works, and maybe, yes I agree with JAMESC359, the model of cable could be a basic without support dor digitals, some adapters or cables support high density, 4k video, 4k+audio, one guy in youtube found the fix with a new displayport cable 4k support.
As per the specification of the cable -
It only support 1080p resolution at 60 Hz. It is clear that your cable is not capable to support higher refresh rate.