I just built this PC, and after installing the drivers I downloaded Deus Ex Mankind Divided to test it out. I was getting the same range of 20-25 fps from ultra to low settings so I think it's a throttling issue. I tried going into wattman to mess with the settings but it started messing up even more so I went back to default. I haven't seen anybody talking about any specific issues/bug fixes for performance in game so I didn't think it was the game.
Here's my specs:
Ryzen 5 2600
Gigabyte RX 580 8GB
16GB of Ram
Asus B450M Mobo
Evga SuperNova 750w G1+ PSU
I have the Radeon Adrenalin software installed with version 18.9.3
I do have the hdmi on the computer plugged into an hdmi split box thing for my other consoles and stuff but I've been using it on everything else and stuff for a while so I didn't think that was the problem but idk.
Any help would be greatly appreciated