Personally, I wouldn't recommend using DVI at all for any resolutions higher than 1080p. Go with the latest revisions of either HDMI or DisplayPort, especially for 4K and higher, and avoid any kind of conversion if possible (go straight HDMI-to-HDMI, or DisplayPort-to-DisplayPort, depending on what your monitor/TV supports).
Secondly, OLED shouldn't affect scaling at all, as it is simply the type of LCD technology used, and the computer's OS is utterly indifferent to that aspect of the display. Individual applications can override the OS's display scaling settings, so you may want to check if Steam is one of them, as it may have its own setting for it.
Lastly, I've been looking for a 4K OLED display, and have had difficulty...