Working as expected on 5.4.0-91-generic and 5.10.0-1052-oem.
$ ldattach HCI /dev/tty ldattach: cannot set line discipline: Operation not permitted
Working as expected on 5.4.0-91-generic and 5.10.0-1052-oem.
$ ldattach HCI /dev/tty
ldattach: cannot set line discipline: Operation not permitted