This and other questions/answers around the web recommend turning off SecureBoot to get
systemctl hibernate to work when encountering the error:
Failed to hibernate system via logind: Sleep verb not supported
How can I get
systemctl hibernate to work as designed (i.e. hibernate/suspend-to-disk) without disabling SecureBoot?
NB: I'd like to avoid
pm-utils unless absolutely necessary. SystemD appears to be the way to do it and there are lots of suggestions that
pm-utils doesn't work well together with SystemD.