Yes, the Canon EOS R3 is compatible with the Delkin Devices PRIME SD V60 128GB.
Canon EOS R3 Slot 2 accepts SD UHS-II. Delkin PRIME SD is Video Speed Class V60 (280/105 MB/s rated) -- meets the 4K 29.97fps ALL-I mode (requires V60) but not the Full HD 239fps slow-motion mode (requires V90).
Limitation
Does not meet Canon R3's Full HD 239fps slow-motion mode (requires Video Speed Class V90) -- this card is V60. Works for 4K 29.97fps ALL-I and all standard SD-slot modes.
“[200 MB/s or higher] Video Speed Class V90 or higher”
Last verified:
Compatibility inferred from spec rule (citations above are manufacturer-verified)