'fastboot flashing unlock' command doesn't work

While trying to install /e/OS on CMF Phone 1 with ADB (on Debian 12), everything is fine until the command 'fastboot flashing unlock'. I get the message < waiting for any device > in return and then nothing else.

The previous command 'adb devices' shows:

List of devices attached 0010134BS001230 device

...so it seems the PC recognizes the phone. However, it doesn't work.

Thank you for your help!