I bought a MacStudio 2 months ago, on Sequoia you go to "display" and should see the various resolutions. If not, "advanced">"show resolutions as a list">"show all resolutions".

Unfortunately, resolutions offered were weird. Native is 5120x2160 but that wasn't offered and scaled resolutions were weird. I guess macOS didn't read monitor's information properly or something. I wasted a few hours frantically trying to figure out how to connect a $12k computer to a 4-year old monitor which should have been a breeze but for some reason wasn't. The same monitor worked fine on Linux or Windows.

Pick up a copy of BetterDisplay. Absolutely useful for monitors with non-standard resolutions.

I feel like this has something to do with Apple fucking with DP 1.4 for the ProDisplay XDR.

My 2019 Mac Pro with Catalina could happily drive 2 4K monitors in HDR @ 144 Hz.

People wondered how Apple got the math to work to drive the ProDisplay.

Big Sur? Not any more. 95Hz for 4K SDR, 60Hz for 4K HDR. Not the cables, not the monitors. Indeed, "downgrading" the monitors advertised support to DP 1.2 gave better options, 120Hz SDR, 75Hz HDR.

And it was never fixed, not in Big Sur, Monterey or Ventura, when I had switched monitors.

Hundreds of reports, hundreds of video/monitor combinations.

Frantically? For hours? If that is what you meant, did you try stepping back for a few minutes, and coming up with a plan / doing research?