You can download and install it in /opt/ so it does not interfere with the currently installed version. Commands:

Download:

wget https://download.java.net/java/GA/jdk18/43f95e8614114aeaa8e8a5fcf20a682d/36/GPL/openjdk-18_linux-x64_bin.tar.gz

Extract the download (replace {version} with the one downloaded):

tar -xvf openjdk-18._linux-{version}

Move it to /opt/:

sudo mv jdk-18* /opt/

(replace jdk-18 to something else if you want) and set the environment variables:

export JAVA_HOME=/opt/jdk-18
export PATH=$PATH:$JAVA_HOME/bin

To check if that went correctly:

cd /opt/jdk-18/
java --version
echo $JAVA_HOME

By re-doing the exports to exclude /opt/jdk-18 you restore the old situation

You cannot install a tar.gz file using dpkg — it's not a .deb package, and dpkg does not know what to do with it.

If you only need to install Java for your user and not systemwide, you could do the following:

tar -xzvf jdk-20_linux-aarch64_bin.tar.gz

This would extract the contents of the archive into a directory called jdk-20.0.2. Now create the .bin/java directory in your home folder:

mkdir -p ~/.bin/java

Now copy the jdk-20.0.2 folder into your new folder:

cp -rp jdk-20.0.2 ~/.bin/java

Now you will need to edit your shell configuration file, it should be .bashrc by default:

nano ~/.bashrc

Add the following lines to this config file:

PATH="$HOME/.bin/java/jdk-20.0.2/bin:$PATH"
export JAVA_HOME=$HOME/.bin/java/jdk-20.0.2

Press Ctrl-o to save the changes and Ctrl-x to exit the editor.

Now you need to source your shell configuration file:

source ~/.bashrc

Verify that you can run the Java VM by using the following command:

java --version

Now you can delete the file you downloaded and the unpacked folder:

rm jdk-20_linux-aarch64_bin.tar.gz
rm -rf jdk-20.0.2/