Yes, the Canon EOS R3 is compatible with the SanDisk Extreme microSDXC UHS-I 128GB.
Canon EOS R3 has a full-size SD card slot. SanDisk Extreme microSDXC UHS-I 128GB (real write speed 130 MB/s, V30-class) fits via the bundled microSD-to-SD adapter and clears the camera's UHS Speed Class 3 modes (4K IPB Standard, standard Full HD), but the camera's own reference page states 4K ALL-I recording requires V60 and 200fps Full HD slow-motion requires V90 -- this V30-class card does not meet either floor; those modes need CFexpress or a genuinely V60/V90-rated SD card.
Conditions for compatibility
requires the bundled microSD-to-SD adapter (included with the card); does not support 4K ALL-I (requires V60) or 200fps Full HD slow-motion (requires V90) -- this card is V30-class. 4K IPB Standard and standard Full HD modes (UHS Speed Class 3) work normally.
Limitation
Cannot record 4K ALL-I or 200fps Full HD slow-motion -- those modes require V60/V90-rated cards; this card is V30-class. IPB Standard 4K and standard Full HD modes work normally.
“4K 59.94 fps 50.00 fps ALL-I IPB (Standard) CFexpress 2.0 UHS Speed Class 3 or higher Video Speed Class V60 or higher IPB (Light) 29.97 fps 25.00 fps 24.00 fps 23.98 fps ALL-I Video Speed Class V60 or higher IPB (Standard) UHS Speed Class 3 or higher IPB (Light) 119.88 fps 100.00 fps ALL-I CFexpress 2.0 Type-B [400 MB/s or higher] Full HD 59.94 fps 50.00 fps ALL-I CFexpress 2.0 UHS Speed Class 3 or higher IPB (Standard) SD Speed Class 10 or higher UHS Speed Class 3 or higher IPB (Light) 29.97 fps 25.00 fps 23.98 fps ALL-I UHS Speed Class 3 or higher IPB (Standard) SD Speed Class 6 or higher IPB (Light) SD Speed Class 4 or higher 239.76 fps 200.00 fps ALL-I CFexpress 2.0 Type-B [200 MB/s or higher] Video Speed Class V90 or higher”
Last verified:
High confidence