When is DisplayPort 2.1 Going to be Used on Monitors?
https://tftcentral.co.uk/articles/when-is-displayport-2-1-going-to-be-used-on-monitors
As a person that will be buying a 4k 240hz OLED in the coming months, this article is very informative and if you are interested, it is worth a read. But to summarize... All current forms of GPU display connections that are out in the market, whether it be DP1.4 on Nvidia, DP2.1 on Radeon or HDMI 2.1 on both will not be able to display 4k 240hz without DSC. The reason is Radeons implementation of DP2.1 isn't full bandwidth. So all display connections will be using some form of DSC, HDMI 2.1 and DP2.1 will use 2:1 ratio while DP1.4 will use 3:1 ratio.
As far as noticeable differences between uncompressed and DSC as well as input lag between them, there is no noticeable difference between uncompressed, 2:1/3:1 ratios. Back in the early days of dp1.4, there were monitors that couldn't display full chroma 4:4:4 so had to go down to 4:2:2 but that's because the DSC implementation wasn't properly done. These days, dp1.4 can do 4k 240hz without any issues and no one will be able to tell the difference between 1.4 + DSC and DP2.1.
The only issue may arise would be black screen or flickering issues if the compatibility between the GPU and monitor isn't done properly but generally those get resolved with firmware updates to the monitor and driver updates to the GPU. Anything beyond the current requirements however such as 4k 360hz, dp1.4 will no longer be viable as the display port even with DSC has reached it's final limits.
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