Confusing these is the commonest reason a service is missing after a reboot. start means run it now; enable means run it at every boot and starts nothing now. You usually want both: enable --now. Its opposite, disable --now, stops the service and removes it from boot.
Under the hood, enable only makes a symlink. WantedBy=multi-user.target in [Install] links the unit into /etc/systemd/system/multi-user.target.wants/, and at boot systemd 142,543 starts everything in that directory on its way to the target (Your Own Unit File shows the symlink). mask links the unit to /dev/null so nothing can start it until you unmask it. systemctl is-enabled is the first check when something did not come back. Ubuntu 225 enables services as their packages install; RHEL-family systems leave them disabled.