Step-by-step – Oracle JDK 11 Installation in Linux Mint 20

Switch

5. 5. Switching to Java 11

   Now to Switch Java to JDK 11
   This is Valid only if you have to Manage more than One Java Releases:

   sudo update-alternatives --config java

And for the Java Compiler instead:

sudo update-alternatives --config javac

Choose the Number entry corresponding to Oracle JDK 11.
Test your Java 11 Installation:

java --version