All the setups I see today is to pop a video card into the desktop that gives us DisplayPort 1.2 or beyond.

No adapter seems to do what you ask so my bet is the reasons are baked into the hardware which I will defer to the makers.

Fix? Just try some adapters, ask the makers (like Startech) or cave and replace the GPU.

PS. Regarding my title message. Yes I see the adapters for sale but no longer in the usual shops because, not much call for these today.