Delayed charge (waiting to charge fully or charging the last ~20% slowly to just-in-time for your alarm) is a different setting, though I don't recall the name for the "Only charge to 80%" one
> To change your charging option with iPhone 15 models and later, go to Settings > Battery > Charging and choose an option. You can choose a charge limit between 80 percent and 100 percent in 5 percent increments.
Probably a combination of the devices being old enough and the battery not being large enough that a lot of people would not find 80% of the already-degraded capacity of their device reasonable, and not wanting to have to explain to customers why their friend’s phone allows it and theirs doesn’t if they both have the same model.
