Relation and differences between spring.jpa.generate-ddl and spring.jpa.hibernate.ddl-auto

For a Spring Boot app (2.4.1) working with Spring Data JPA, with @Entity classes based with the javax.persistence annotations. For a application.properties exists these two properties:

• spring.jpa.generate-ddl
• spring.jpa.hibernate.ddl-auto

Thanks to STS, the following descriptions are available:

spring.jpa.generate-ddl

spring.jpa.generate-ddl
java.lang.Boolean

Default: false

Whether to initialize the schema on startup.

spring.jpa.hibernate.ddl-auto

spring.jpa.hibernate.ddl-auto
java.lang.String

DDL mode. This is actually a shortcut for the "hibernate.hbm2ddl.auto" property. 
Defaults to "create-drop" when using an embedded database and no schema manager was detected. 
Otherwise, defaults to "none"

• When is used the spring.jpa.generate-ddl?
• When is mandatory use the spring.jpa.generate-ddl approach? What scenario?

I did realise that it is ignored and really is mandatory use spring.jpa.hibernate.ddl-auto, it for the following scenario: The schema is created through the schema.sql file for H2 and spring.jpa.hibernate.ddl-auto is none, in this case spring.jpa.generate-ddl is totally ignored

Therefore:

What is the relation (if exists) and differences between spring.jpa.generate-ddl and spring.jpa.hibernate.ddl-auto?

I found these posts, and in someway is not clear when is mandatory use spring.jpa.generate-ddl

• H2 schema still generated when spring.jpa.generate-ddl=false
• Hibernate Annotation relations does not work with spring.jpa.generate-ddl=true
• tables not creating in spring boot v2.2.6.RELEASE postgres