No, the Canon EOS R3 is not compatible with the Transcend 700S V90 128GB.
Canon EOS R3's own performance table states its highest-bitrate SD-recordable mode (Full HD 239.76fps ALL-I) requires 200 MB/s or higher (Video Speed Class V90 or higher) -- a raw floor, not satisfied by V90 class alone. Transcend 700S's real manufacturer-rated write speed is 180 MB/s (corrected 2026-07-10 from a previously-stored 250 MB/s that didn't match any real source) -- falls short of that 200 MB/s floor. Incompatible for this specific mode; other SD-recordable modes on the R3 aren't independently sourced here.
What works instead
See all compatible camera for the Canon EOS R3 →“[200 MB/s or higher] Video Speed Class V90 or higher”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)