Is this a laptop or desktop with a discrete card? Need your system information.
Have you gone to the AMD Support page and downloaded and installed the Auto Detect application. The only two VEGA drivers I see are VEGA 64 and VEGA 56. If all else fails I would try one of these drivers, the 64 one first.
If you go to https://www.techpowerup.com/gpu-specs/radeon-vega-8.c3042 you will find all of the specs for that card. Why it doe's not show up in the legacy drivers I have no idea.
If it ain't broke; don't fix it!