When IntelliJ IDEA is installed, Kotlin applications cannot be compiled or run unless the Java SDK is installed. Choose to get the Oracle Java SDK or install the OpenJDK SDK corresponding to the OpenJDK Java Runtime Environment that has been installed.
By default, the Linux distribution will just install the Java Runtime Environment (JRE). To work with Java applications, Java SDK must be installed too for the version of the Java Runtime Environment that has been installed.
To find the Java version on the computer, open a terminal window and enter:
$ java --version <enter>
openjdk 11.0.7 2020-04-14
OpenJDK Runtime Environment (build 11.0.7+10-post-Ubuntu-3ubuntu1)
OpenJDK 64-Bit Server VM (build 11.0.7+10-post-Ubuntu-3ubuntu1, mixed mode, sharing)
Corresponding to the output shown, install the java SDK. In above case, it would be OpenJDK 11:
$ sudo apt-get install openjdk-11-sdk <enter>
Now start IntelliJ IDEA and Java would be functional.