My other major contention is that Display Stream Compression has been broken since .0 betas through .1.
I have 2 27" 4K HDR 144Hz monitors.
On Catalina I can drive them at full spec on my 2019 Mac Pro, with a W5700X.
On Big Sur, my options are HDR @ 60Hz, or SDR @ 95Hz.
Not to mention the monitors also got a firmware update to unlock 165Hz, which neither Catalina or Big Sur recognize.