Odoo 19.0 was released last week.

What you are asking about is the ability to upgrade an older database.

The upgrade will be available to test in October for Odoo Online Customers, available later in November for Odoo.sh and Odoo On Premise Customers.

This is based on what we know today, we may adjust these dates if we cannot provide a high quality upgrade experience.  Until we start upgrading databases we do not have enough information to predict if our scripts will need much adjusting.