You need two adapters and a cable for a DV FireWire camcorder:
Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter
Apple Thunderbolt to FireWire Adapter
FireWire 800 9-pin to 400 4-pin cable
I initially used my old FireWire 800 drives with Mac mini 2018 (Mac mini's Thunderbolt 3 (USB-C) port – Thunderbolt 3 to Thunderbolt 2 adapter – Thunderbolt to FireWire adapter - FW800 to FW800 (or FW400) cable - FireWire drive).
I also briefly tried my old D8 (essentially the same as miniDV except it uses Hi8 tapes instead miniDV tapes) Sony TRV320E (unnEUtered to allow analog-in and analog-to-DV passthrough so I could use it to digitize all old VHS footage as well) and it worked quite OK in Mojave and iMovie HD 6.0.3 although occasionally I had to reconnect the cable to make it work. I have an old Mac mini 2009 and also PowerBook G4 2004 for DV work but I have essentially retired the DV gear by now.
But now I have retired that old Firewire gear.