Yes, the Canon EOS R8 is compatible with the SanDisk Extreme PRO SD UHS-II V90 128GB.
Canon EOS R8 has an SD UHS-II slot with a Video Speed Class V60 floor for its top-tier 4K60 IPB (Standard) mode. This card clears both the 4K30 (30 MB/s) and 4K60 (60 MB/s) floors — compatible for every recording mode including the camera's highest-bitrate codec. SanDisk Extreme PRO SD UHS-II V90 128GB is V90 class. Meets the floor for: 4K30 (30 MB/s floor); 4K60 (60 MB/s floor). (Peak write 304 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)