Dude this is a bug in fastboot. When this happens, close the command line, unplug the usb cable and reboot the phone in fastboot mode. Then try different usb ports. You may need to do this a few times. Don't worry, nothing will happen to your data.
https://xiaomi.eu/community/threads/installing-a-custom-recovery.67841/
Post in thread '23.1.3' https://xiaomi.eu/community/threads/23-1-3.67827/post-681352
https://xiaomi.eu/community/threads/installing-a-custom-recovery.67841/
Post in thread '23.1.3' https://xiaomi.eu/community/threads/23-1-3.67827/post-681352