It would be very helpful if a sticky topic could be put at the top of the forum that points to the latest version of the manual, and that is kept updated.
David, you’ve still not found the most recent manual. See Dorico Pro 3 Documentation
Note that you can get to the correct version of the online manual from the Help menu in Dorico.
There seems to be no information on “Condensing” in the Dorico 3 manual itself.
Despite the link within Dorico, I still think a sricky one here would be useful. This is my go-to website, since the main Steinberg site is not over user-friendly in this respect.
The place to get the most up to date information about any new features is always the Version History PDF, which has about 12 pages of information on condensing.