I also have problems with uniformity as
@Simoner described with my Nano XDR on solid colors. Additionally the right upper corner is darker as the rest (confirmed by measuring with a colorimeter).
I’ve already arranged a replacement with Apple, tried to negotiate for a replacement in advance (so I’m not without screen), but Apple wouldn’t do this but promised a replacement in 5 business days. The day the defect XDR was scheduled for pick up, I’ve got a call from Apple that the replacement would take at least until mid March so I refused to send out the display and am waiting for new information from Apple.
Very disappointed for such a expensive display (uniformity) and the way replacements are handled. I assumed this would be handled better with Apple Care+
If the replacement shows similar problems with uniformity I’ll consider a return and will get a NEC or EIZO with digital uniformity control.