Can't import java.lang.module.ModuleDescriptor.Version

You are not changing the Java version for your project - you are changing the Java version that Gradle should use (as indicated by the "Gradle JVM" label before the dropdown selector).

If you want your project to use Java 18 you must change it under "File" -> "Project Structure" (which opens the Project Settings) and there under the tab "Project", entry "SDK".

As per the docs https://docs.oracle.com/javase/9/docs/api/java/lang/module/ModuleDescriptor.html

ModuleDescriptor is in JDK 1.9 . You can download JDK from here https://www.oracle.com/ca-en/java/technologies/javase/javase9-archive-downloads.html

then import it in your android studio.

ModuleDescriptor is exists for the JAVA SE 9 & JDK 9. read the documentation at official website