This is not an official support, but Dorico Pro 3 runs on Windows 7.
According to my tests on my customized Windows Embedded 7 x64 build, Dorico Pro 3 still runs well.
My Embedded system build is a slimed version of Windows 7 SP1 with platform update included.
As usual: Windows Aero Glass effect (whether transparent or not) must be enabled, plus the Windows 7 platform update.
This shall work with Windows 7 SP1 (with Platform Update) Ultimate / Professional / Home Premium / Home Basic.
Regarding how to enable Windows Aero on Windows 7 Home Basic, please check those sticked threads in this sub-forum.
If using Windows Embedded 7 x64, make sure you installed the full desktop experience (at least the DWM is required to make sure Windows Aero is enable-able) AND “WDM Class-Compliant USB Audio Driver”!!! If having lack of the driver, some USB audio interface may not work even if their factory drivers are installed!!! (This is a common topic regarding Windows Embedded 7.)