Configure VM serial socket
On the host modify the VM configuration file
vi /etc/pve/qemu-server/125.conf
serial0: socket
Configure guest VM
vi /etc/default/grub
GRUB_CMDLINE_LINUX="quiet console=tty0 console=ttyS0,115200"
Update grub and verify that the console is working during reboot
update-grub
reboot
On the host connect to the serial console
qm terminal 125