Modem stopped working out of the blue

[Martin]

Hi,

my modem used to work until recently, but suddenly (and without any
software update, at least intentionally), I get:

$ sudo mmcli --modem=0 --messaging-list-sms
error: modem not enabled yet
$ sudo mmcli --modem=0 --enable
error: couldn't enable the modem:
'GDBus.Error:org.freedesktop.libqmi.Error.Protocol.MissingArgument:
Couldn't register for power indications: QMI protocol error (17):
'MissingArgument''

Software versions are:

libmbim-glib4 1.28.0-1~bpo11+1
libmbim-proxy 1.28.0-1~bpo11+1
libmbim-utils 1.28.0-1~bpo11+1
libmm-glib0   1.20.0-1~bpo11+1
libqmi-glib5  1.32.0-1~bpo11+1
libqmi-proxy  1.32.0-1~bpo11+1
libqmi-utils  1.32.0-1~bpo11+1
modemmanager  1.20.0-1~bpo11+1

Status says: "lock: sim-pin2".

Any idea, what might be wrong?

TIA!