Hello forum
I received an answer from product management, it's 4K capable:
"the PXIe-8821 DP outputs are capable of driving 4K (3840x2160) @ 60Hz.
In case a customer isn’t seeing that resolution, it could be because of an old driver or even a bad DP cable. A x4 HBR link is required for that resolution, and a bad cable might limit link speed and or link width."
Cheers, Raphael