Yes, the Canon EOS R8 is compatible with the Transcend 700S V90 64GB.
Transcend 700S V90 is V90 class. Meets the floor for: 4K30 (30 MB/s floor); 4K60 (60 MB/s floor). (Rated write 180 MB/s is not evidence of sustained performance; the V90 class rating above decides this.)
“IPB (Standard) UHS Speed Class 3 or higher Video Speed Class V60 or higher IPB (Light) UHS Speed Class 3 or higher”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)