Indesing 16.4

it's in your cc desktop app > id > install other versions.

if you don't see that, change your preferences to show older apps:

https://helpx.adobe.com/it/download-install/using/install-previous-version.html

To change the language of the link above, type "en" or "es" instead of "it"

Adobe only supports the last two versions of CC apps. So with the release of version 18 you won't be able to download version 16 using Creative Cloud Desktop app, you might be in luck as the version 18 is just rolling so do check your Creative Cloud Desktop app.

Install previous versions of your Creative Cloud apps - Adobe Inc.

If you don't find the download option then the only way is to contact Adobe and ask them for a download link, they might do so.

To contact support follow the instructions given below
1. Go to https://helpx.adobe.com/contact.html?rghtup=autoOpen
2. Wait a bit on the page that opens up, it should automatically open a chat popup. If that does not happen then look for a call out/chat icon at the bottom right, click over it and the chat popup should open
3. In order to talk to a human type "AGENT" in the chat box
4. If you are not able to get to the chat window, then disable your adblockers, firewall, enable cookies/scripts on your browser. If it still fails then change your browser/machine/network.

P.S. Be mindful of answering anyone who sends you a private message. See the following for more information about scammers
https://tinyurl.com/y7cfrr7y
-Manan