This Graphics Adapter wasn't Wasn't validated by Intel or Zotac for NUC9i9QNX (although it still may work on it, just it wasn't tested). I suggest that you check the list of Intel and/or Manufacturer verified components for NUC9i9QNX.
Following the above list should assure the compatibility.
The smallest 2070 Super cards are supposed to fit but when I tried the clearance was so bad that I relented and went with a 2060 that was about .5 inches shorter. Its tight, but acceptable.
I don't think this is going to matter though looking at the Nvidia gen 3000 cards. I suspect that even low end cards will outperform the 2070. The performance : Watt ratio is also much better so getting 2080 performance for 2060 power consumption should be more or less accurate, and cheaper than a 2070.
Just need to wait for the smaller builds to come out, should be before the year is up.
There is technically less than 8" for the card and most of the dual-fan cards are just slightly longer than that. I also chose to go with a single-fan 2060 card instead; the theory being that 2070 may require two fans to adequate cool it.
I have installed a Zotac 1660 Ti with dual fans. It fit nicely without any issues. Now, I have not powered up yet (waiting for memory and storage), but I expect no problems.