Not sure what you are talking about. The docs say this:
The state, including attributes, of trigger-based sensors and binary sensors is restored when Home Assistant is restarted. The state of other trigger-based template entities is not restored.
And that is exactly what happens for all my triggered template sensors.
The state was unknown because HA was off and not monitoring it. Then the state is changed to the last known value.
This is how home assistant works at a very deep level. It is unlikely to be changed.
I have a template sensor that computes a value once a day. If I restart Home Assistant, that value is lost. I don’t want to recompute on restart as the value will change during the day due to source sensor changes.