Oh, and if you want to utilize 120Hz on the XDR display, you're going to have to replace your perfectly functioning Mac.
> Mac models with M1, M1 Pro, M1 Max, M1 Ultra, M2, and M3 support Studio Display XDR at up to 60Hz. All other Studio Display XDR features are supported.
I don't really see your point. The chips mentioned do not have enough bandwidth on display outputs to support the monitor at 6K@120Hz. If anything, I find it surprising that Apple supports running the display in 60Hz mode instead of telling people to go pound sand and buy new Macs.
Almost certainly due to bandwidth limitations on older versions of Thunderbolt. Full bit depth HDR 5k @ 120hz requires some absurd data thoughput.