TYPO3 v9 has reached its end-of-life September 30th, 2021 and is not maintained by the community anymore. Looking for a stable version? Use the version switch on the top left.
You can order Extended Long Term Support (ELTS) here: TYPO3 ELTS.
https://docs.google.com/document/d/1CqSgEgxnWwq8GT31kawGSVJp7hfU2TcVe9BAbtzFK0A/edit# - ACME architecture document 2015-07 Nueremberg