You can suspend a VM to disk with the GUI option Hibernate
or with
# qm suspend ID --todisk
That means that the current content of the memory will be saved onto disk and the VM gets stopped. On the next start, the memory content will be loaded and the VM can continue where it was left off.
State storage selection. If no target storage for the memory is given, it will be automatically chosen, the first of:
vmstatestorage
from the VM config.
local
as a fallback.