No, the Nikon Z8 is not compatible with the Transcend 700S V90 64GB.
Nikon Z8 Slot 2 accepts SD UHS-II. Nikon's own Approved Memory Cards page states SD cards need an actual 250 MB/s write speed for high frame size/rate video -- a raw floor, not just a V90 class label. Transcend 700S's real manufacturer-rated write speed is 180 MB/s -- falls short by 70 MB/s. Incompatible for the Z8's high frame size/rate SD-recordable modes.
What works instead
See all compatible camera for the Nikon Z8 →“are recommended for recording and playback of videos with a high frame size or rate”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)