This seems to confirm my suspicion that for whatever reason, the XDR is handling onboard graphics different than even the refreshed Studio Display (2026) and that it has nothing to do with what cable you use at all. My Dell Latitude 3520 with Intel Iris Pro graphics ran at 5K 60hz using the Thunderbolt 5 cable that comes with the display on the demo unit at the Apple Store last week. And that's just from a DisplayPort 1.4 spec on a Windows machine. But on the Studio Display XDR it could not go above 1080p 60 oz. It is deeply frustrating to me that a display that costs twice as much has far more limiting output capabilities as it stands right now. I'm really hoping this can be addressed with future firmware. I wonder how frequently the demo units in store get these firmware updates. I'm thinking of going back in with my Dell work laptop and my M1 Pro MacBook and playing around some more.
The standstill I'm at here is the regular Studio Display somehow feels even more outdated at it's price point now (unless you care about a new webcam, which isn't a reason to upgrade by itself) when you consider what you can get instead with LG or Asus with those LCD panel specs, especially if you want that tilt and raise stand. It's a monitor that just sits at an extremely weird place in the segment now that Apple offers two versions. All in for the regular SD, you're paying $2,000 for visuals you've largely been able to get for half that price for quite a while now. It was a question of that glossy panel and aesthetics. Whereas the XDR comes with that premium stand already (we'll call it $2900 for the display by itself) and you're future proofing yourself a lot more with mini-LED, Thunderbolt 5 and 120 hz. The idea of having a 27-inch version of my MacBook Pro display is very tempting, because it's stunning. Part of me thinks that if you are already prepared to pay $2,000, that extra $1,000 buys a lot more peace of mind five years from now. And I think Apple is counting on the enthusiasts to do these mental gymnastics so they end up going with the Studio Display XDR.