Hi,
sorry for the delay, I had only seen this thread today. :-[
Use this for the moment:
https://web.archive.org/web/20220809164846/https://jdownloads.net/documentation-for-v3-9/getting-started-v3-9/upgrading-from-jdownloads-3-2-to-3-9
We work still on a new documentation structure with Joomla 4. ::) :-\