Not on Ubuntu, but the following works for me:
systemd-inhibit --what sleep --why "Lock screen" --mode delay xdg-screensaver lock & systemctl suspend
xdg-screensaver lock with the command to lock the screen on your system and
systemctl suspend with
systemctl hibernate if you want to lock the screen before hibernating.
This works by locking the screen in parallel to suspending the machine. However the screen locking command is running as inhibitor that delays the sleep. This way, systemd will wait until the screen is locked before executing.
If you have inhibitors that are blocking the suspend, add the
-i flag at the end.