(I think) what you are thinking of was something introduced around the Catalina>Big Sur transition, when the Pro Display XDR was introduced.

At the time, people were "marveling" at the magic of Apple, and wondering how they did the math to make that display work within bandwidth constraints.

The simple answer was "by completely fucking with DP 1.4 DSC".

I had at the time a 2019 (cheesegrater) Mac Pro. I had two Asus 27" 4K HDR 144Hz monitors, that the Mac had no problems driving under Catalina.

Install Big Sur. Nope. With the monitors advertising DP 1.4, my options were SDR@95Hz, HDR@60Hz. I wasn't the only one, hundreds of people complaining, different monitors, cards, cables.

I could downgrade to Catalina: HDR@144Hz sprung back to life.

Hell, I could on the monitors tell them to advertise DP 1.2 support, which actually improved performance, and I think I got SDR@120Hz, HDR@95Hz (IIRC).

So you don't deserve downvotes on this. Apple absolutely ignored standards and broke functionality for third party screens just to get the Pro Display XDR (which, ironically, I own, although now it's being driven by an M2 Studio, versus the space heater that was the Xeon cheesegrater).