Whatever Apple is doing for the XDR (which I own) is not DSC, or not standard.
Because DSC has been broken ever since the Big Sur betas. Catalina supported 1.4 and DSC and my cheese grater Mac Pro happily drove 2x27" 4K monitors in HDR @ 144Hz.
Big Sur? Nope, you get 95Hz SDR or 60Hz HDR. If you set the monitors to DP1.2 you get 120Hz SDR.