You can contact Adobe Support directly to request an installer for an older version if your workflow or operating system requires it.
Platforms like ProDesignTools traditionally host direct download links to Adobe's own servers for versions up to 2019.
While version 23 is no longer a standard download, you may still find it through these methods:
Downloading has become more difficult recently because Adobe's official policy is to only support the current version and one major version prior. Consequently, older versions like 2019 are typically removed from the Creative Cloud desktop app once they fall out of this window. How to Access Illustrator 2019 v23