Are you trying to install Ghidra for one user, or Ghidra server for multi user collaboration?
That link is for the latter. For the former just download the release zip from https://ghidra-sre.org/.
Ensure you have Java 11, no older, no newer. You must use Java 11. It also must be the JDK (ie, you need to have 'javac' sitting next to 'java')
If you need to you can point it at a specific JAVA_HOME in case you want to just extract AWS Corretto 11 into a directory and not use Java11 for your whole system. Works flawlessly for me.
Note in the document the small section starting with "In some cases, you may want Ghidra to launch with a specific version of Java instead of the version that Ghidra automatically locates" - I recommend you this method.
The only official sites are ghidra-sre.org and the GitHub page. I really wish they'd host their docs on their site since there is clearly a demand for it, but unfortunately they don't.