Is it better to keep an EV at 80% or to leave it between 50% and 80% for weeks?

Instead of 80% I'd say optimal voltage but I don't know what that is, and the car doesn't show me the battery voltage.

Why isn't there a setting to charge to optimize battery longevity? Even if that means the battery is at 70% or 75% or whatever.

Often I get home with 60%. Should I wait until I get home with < 50% before charging? Or just keep it at 80%?