About battery health

is it true that I charge the iPhone from 30% to 80% to preserve the battery

No, you will do better if you make sure that Optimized Battery Charging is enabled and simply plug the phone into the adapter and let it go all night, every night.

Then, charge the phone as needed during the day.

Do the same for the laptop.

No, that is not correct.

Turn on Optimize Battery Charging and let your device manage battery health on its own. Plug it when possible. Nothing you can do manually will do any better.