Which FireWire cable do I need to connect an iMac (late 2009) to a Thunderbolt to FireWire connection to retrieve the data using Diskmode?
The iMac 2009 has a FireWire 800 port and the new iMac 2019 a Thunderbolt 3 port.

This requires three cables daisy-chained:


FireWire 800 - FireWire 800
FireWire 800 - Thunderbolt 1/2: Apple Thunderbolt-naar-FireWire-adapter
Thunderbolt 1/2 - Thunderbolt 3: Adapter voor Thunderbolt 3 (USB‑C) naar Thunderbolt 2


I found one source stating it's working: Le Target Disk Mode marche en USB-C, en Thunderbolt et en FireWire (en français, with pics) and another one stating more or less the opposite: Target mode between Macbook pro 2017 and Mac Pro 1.1.