I can't get my R3 to use any shutter above 1/8000. I am using an EF adapter with a Canon 35mm F2.0 lens. I have the camera set to electronic shutter and I have set the maximum shutter speed to 1/64000 in the menus. I have tried in both manual and Tv mode and I can't get it to work. I have tried at various aperture setting with no luck. I have done a Google search without any satisfactory results. I hope someone knows the answer and thanks for all your help.
Can you please confirm what firmware version you are using?
You may be limited by the fact you are using EF lenses and an adapter, rather that native RF lenses. I have not seen any reference to tthisability for legacy lenses.