System (Java) properties, if they start with

org.gradle.project.

, are added as Gradle properties to the project (without the prefix)

environment variables, if they start with

ORG_GRADLE_PROJECT_

, are similarly added as Gradle properties to the project (without the prefix)

System properties can be set with

./gradlew -D...

or similar through JVM options; Gradle properties can be set with

./gradlew -P...

or

gradle.properties

so there is no need for the prefix on Gradle properties; you just need it on system properties if you want to use that mechanism to set Gradle properties

there was a recent blog post about this: https://www.liutikas.net/2022/04/25/A-Bag-Of-Properties.html