Runtime
You can use a specific Java version by creating a file called system.properties in the root level of your application with the following content:
java.runtime.version=20
Accepted major version values are 1.8, 11, 13, 15, 17, 19, and 20.
If you do not specify a Java version, the default value is set to 1.8
I modified the system.properties file by referring to the above, but it is still built with 1.8.
I am using gradle, is this the cause?
1.8 builds successfully with gradle