I have tried multiple releases from here using :
sudo -i
cd /usr/lib/jvm
wget [release link here]
tar xzf [file name here]
export PATH=$PWD/[dir here]/bin:$PATH
java -version
But after java -version I always get:
/usr/lib/jvm/[dir here]/bin/java: cannot execute binary file: Exec format error
Which means I have chosen the wrong release/architecture. Is there a release that works with Raspberry Pi's or is there another way to install Java 16?
Answering my own question.
cd [minecraft directory here]
wget https://github.com/AdoptOpenJDK/openjdk16-binaries/releases/download/jdk16u-2021-05-08-12-45/OpenJDK16U-jdk_arm_linux_hotspot_2021-05-08-12-45.tar.gz
tar xzf OpenJDK16U-jdk_arm_linux_hotspot_2021-05-08-12-45.tar.gz
export PATH=$PWD/jdk-16.0.1+4/bin:$PATH
java -version
You might have to do
export PATH=$PWD/jdk-16.0.1+4/bin:$PATH
after a reboot