This topic has been discussed a lot and I also would like to have such feature, but the main issue is the risk of partial updated due to user shutting down (or sleep) the pc in the middle of an update.
Long back I tried to implement a solution using "systemd-inhibit", but it didn't work since at that time the inhibitor could not stop the user will. Then I tried for some time reboot guard which worked in principle, but not perfect and is not maintained anymore.
So as of today, I follow the recommended manual update way, since the effort to get a reliable low risk automatic update was too big.