Firmware version 1.1.0 for the EOS R1 and EOS R5 Mark II, announced early in July 2025, is currently unavailable. "Canon has determined that playback may not be possible on the camera or a PC when users are shooting videos with pre-recording settings using a card reader larger than 2TB. Canon is taking steps to have the firmware available as soon as possible."
If you have already downloaded the firmware, Canon advises that you do not install it on your camera.