Just to let u know, OS boots normally and finds GPU as RX5700 XT, I used phoenixminer and it started to mine but with 0MH/s. tried to OC/UV but OS freezes right away.
Yeah, i also tested it and i checked what is wrong.
Phoenix does not support RX5700XT gpu on linux. It only supports it on windows

I found miner that support this gpu and it is wildrig, als xmrig or stack should support this gpu.
Anyway under linux there is still not so much support, probably due to very low profitability

Well, Phoenixminer do support it under Linux, it is rather a driver issue with NAVI support. As for the profitability these cards are almost 100% better than RX580 doing 52MH/s at 92W. Unfortunately that will not last as ETH2.0 is coming next year...