Resolved! EOS R5C will not update firmware: “check the power supply”
My Canon EOS R5 C came with firmware version 1.0.5.1 installed. I have the 1.0.6.1 firmware file on the formatted SDXC (v90) card. The R5C sees it and will open the Version 1.0.5.1 -> Version 1.0.6.1 update screen, but the “OK” button is greyed out...